[Show abstract][Hide abstract] ABSTRACT: Overcoming the notorious apoptotic resistance of melanoma cells remains a therapeutic challenge given dismal survival of patients with metastatic melanoma. However, recent clinical trials using a BRAF inhibitor revealed encouraging results for patients with advanced BRAF mutant bearing melanoma, but drug resistance accompanied by recovery of phospho-ERK (pERK) activity present challenges for this approach. While ERK1 and ERK2 are similar in amino acid composition and are frequently not distinguished in clinical reports, the possibility they regulate distinct biological functions in melanoma is largely unexplored.
Rather than indirectly inhibiting pERK by targeting upstream kinases such as BRAF or MEK, we directly (and near completely) reduced ERK1 and ERK2 using short hairpin RNAs (shRNAs) to achieve sustained inhibition of pERK1 and/or pERK2.
Using A375 melanoma cells containing activating BRAFV600E mutation, silencing ERK1 or ERK2 revealed some differences in their biological roles, but also shared roles by reduced cell proliferation, colony formation in soft agar and induced apoptosis. By contrast, chemical mediated inhibition of mutant BRAF (PLX4032) or MEK (PD0325901) triggered less killing of melanoma cells, although they did inhibit proliferation. Death of melanoma cells by silencing ERK1 and/or ERK2 was caspase dependent and accompanied by increased levels of Bak, Bad and Bim, with reduction in p-Bad and detection of activated Bax levels and loss of mitochondrial membrane permeability. Rare treatment resistant clones accompanied silencing of either ERK1 and/or ERK2. Unexpectedly, directly targeting ERK levels also led to reduction in upstream levels of BRAF, CRAF and pMEK, thereby reinforcing the importance of silencing ERK as regards killing and bypassing drug resistance.
Selectively knocking down ERK1 and/or ERK2 killed A375 melanoma cells and also increased the ability of PLX4032 to kill A375 cells. Thus, a new therapeutic window is open for future clinical trials in which agents targeting ERK1 and ERK2 should be considered in patients with melanoma.
Journal of Translational Medicine 01/2012; 10(1):15. DOI:10.1186/1479-5876-10-15 · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Interleukin-23 is a key cytokine involved in the generation of Th17 effector cells. Clinical efficacy of an anti-p40 mAb blocking both IL-12 and IL-23 and disease association with single nucleotide polymorphisms in the IL23R gene raise the question of a functional role of IL-23 in psoriasis. In this study, we provide a comprehensive analysis of IL-23 and its receptor in psoriasis and demonstrate its functional importance in a disease-relevant model system. The expression of IL-23 and its receptor was increased in the tissues of patients with psoriasis. Injection of a mAb specifically neutralizing human IL-23 showed IL-23-dependent inhibition of psoriasis development comparable to the use of anti-TNF blockers in a clinically relevant xenotransplant mouse model of psoriasis. Together, our results identify a critical functional role for IL-23 in psoriasis and provide the rationale for new treatment strategies in chronic epithelial inflammatory disorders.
The Journal of Immunology 10/2010; 185(10):5688-91. DOI:10.4049/jimmunol.1001538 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The protein encoded by paired-box homeotic gene 3 (PAX3) is a key regulator of the microphthalmia-associated transcription factor (Mitf) in the melanocyte lineage. Here, we show that PAX3 expression in skin is directly inhibited by TGF-beta/Smads. UV irradiation represses TGF-beta in keratinocytes, and the repression of TGF-beta/Smads upregulates PAX3 in melanocytes, which is associated with a UV-induced melanogenic response and consequent pigmentation. Furthermore, the TGF-beta-PAX3 signaling pathway interacts with the p53-POMC/MSH-MC1R signaling pathway, and both are crucial in melanogenesis. The activation of p53-POMC/MSH-MC1R signaling is required for the UV-induced melanogenic response because PAX3 functions in synergy with SOX10 in a cAMP-response element (CRE)-dependent manner to regulate the transcription of Mitf. This study will provide a rich foundation for further research on skin cancer prevention by enabling us to identify targeted small molecules in the signaling pathways of the UV-induced melanogenic response that are highly likely to induce naturally protective pigmentation.
[Show abstract][Hide abstract] ABSTRACT: IFN-inducible IFI16 protein (encoded by IFI16 gene at 1q23.1) is the human member of the IFN-inducible structurally related p200 family proteins. Increased expression of the IFI16 protein, a positive modulator of p53-mediated transcription, in normal old human diploid fibroblasts (HDF) is associated with cellular senescence-mediated cell growth arrest. However, the underlying mechanisms that contribute to transcriptional activation of the IFI16 gene in old HDFs remain to be elucidated. Here, we reported that functional activation of p53 in normal young HDFs and p53-null Saos2 cell line resulted in transcriptional activation of the IFI16 gene. We identified a potential p53 DNA-binding site (indicated as IFI16-p53-BS) in the 5'-regulatory region of the IFI16 gene. Importantly, p53 bound to IFI16-p53-BS in a sequence-specific manner in gel-mobility shift assays. Furthermore, p53 associated with the 5'-regulatory region of the IFI16 gene in chromatin immunoprecipitation assays. Interestingly, p53 associated with the regulatory region of the IFI16 gene only on treatment of cells with DNA-damaging agents or in the old, but not in the young, HDFs. Importantly, our promoter-reporter assays, which were coupled with site-directed mutagenesis of IFI16-p53-BS, showed that p53 activates transcription of the IFI16 gene in HDFs through the p53 DNA-binding site. Together, our observations provide support for the idea that up-regulation of IFI16 expression by p53 and functional interactions between IFI16 protein and p53 contribute to cellular senescence.
Molecular Cancer Research 12/2008; 6(11):1732-41. DOI:10.1158/1541-7786.MCR-08-0208 · 4.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Studies have identified IFN-inducible Ifi202 gene as a lupus susceptibility gene (encoding p202 protein) in mouse models of lupus disease. However, signaling pathways that regulate the Ifi202 expression in cells remain to be elucidated. We found that steady-state levels of Ifi202 mRNA and protein were high in mouse embryonic fibroblasts (MEFs) from E2F1 knockout (E2F1(-/-)) and E2F1 and E2F2 double knockout (E2F1(-/-)E2F2(-/-)) mice than isogenic wild-type MEFs. Moreover, overexpression of E2F1 in mouse fibroblasts decreased expression of p202. Furthermore, expression of E2F1, but not E2F4, transcription factor in mouse fibroblasts repressed the activity of 202-luc-reporter in promoter-reporter assays. Interestingly, the E2F1-mediated transcriptional repression of the 202-luc-reporter was independent of p53 and pRb expression. However, the repression was dependent on the ability of E2F1 to bind DNA. We have identified a potential E2F DNA-binding site in the 5'-regulatory region of the Ifi202 gene, and mutations in this E2F DNA-binding site reduced the E2F1-mediated transcriptional repression of 202-luc-reporter. Because p202 inhibits the E2F1-mediated transcriptional activation of genes, we compared the expression of E2F1 and its target genes in splenic cells from lupus-prone B6.Nba2 congenic mice, which express increased levels of p202, with age-matched C57BL/6 mice. We found that increased expression of Ifi202 in the congenic mice was associated with inhibition of E2F1-mediated transcription and decreased expression of E2F1 and its target genes that encode proapoptotic proteins. Our observations support the idea that increased Ifi202 expression in certain strains of mice contributes to lupus susceptibility in part by inhibiting E2F1-mediated functions.
The Journal of Immunology 06/2008; 180(9):5927-34. DOI:10.4049/jimmunol.180.9.5927 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Creation and maintenance of psoriatic plaques require a multicellular conspiracy by which prepsoriatic skin becomes infiltrated by a variety of immunocytes triggering changes in the behavior of epidermal keratinocytes and endothelial cells. These complex cellular events require coordination in space and time to achieve the mature plaque. Key molecular coordinators dictating behavior and movement of cells within plaques include cytokines as well as chemokines. These mediators of inflammation play fundamentally important roles in the pathophysiology of psoriasis. The purpose of this chapter is to provide an updated review of cytokine and chemokine networks in psoriatic skin lesions.
Clinics in Dermatology 11/2007; 25(6):568-73. DOI:10.1016/j.clindermatol.2007.08.011 · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: By deciphering the dysregulation of apoptosis in melanoma cells, new treatment approaches exploiting aberrant control mechanisms regulating cell death can be envisioned. Among the Bcl-2 family, a BH3-only member, NOXA, functions in a specific mitochondrial-based cell death pathway when melanoma cells are exposed to a proteasome inhibitor (e.g., bortezomib). Some therapeutic agents, such as bortezomib, not only induce proapoptotic Bcl-2 family members and active conformational changes in Bak and Bax but also are associated with undesirable effects, including accumulation of antiapoptotic proteins, such as Mcl-1. To enhance the bortezomib-mediated killing of melanoma cells, the apoptotic pathway involving NOXA was further investigated, leading to identification of an important target (i.e., the labile Bcl-2 homologue Mcl-1 but not other survival proteins). To reduce Mcl-1 levels, melanoma cells were pretreated with several different agents, including Mcl-1 small interfering RNA (siRNA), UV light, or the purine nucleoside analogue fludarabine. By simultaneously triggering production of NOXA (using bortezomib) as well as reducing Mcl-1 levels (using siRNA, UV light, or fludarabine), significantly enhanced killing of melanoma cells was achieved. These results show binding interactions between distinct Bcl-2 family members, such as NOXA and Mcl-1, in melanoma cells, paving the way for novel and rational therapeutic combination strategies, which target guardians of the proapoptotic Bak- and Bax-mediated pathways, against this highly aggressive and often fatal malignancy.
Cancer Research 11/2006; 66(19):9636-45. DOI:10.1158/0008-5472.CAN-06-0747 · 9.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Increased expression of p202 protein (encoded by the Ifi202 gene) in splenocytes derived from B6.Nba2 mice (congenic for the Nba2 interval derived from the New Zealand Black mice) was correlated with defects in apoptosis of splenic B cells and increased susceptibility to develop systemic lupus erythematosus. We have now investigated the molecular mechanisms by which increased expression of p202 in B6.Nba2 cells contributes to defects in apoptosis. In this study, we report that increased expression of p202 in the B6.Nba2 splenocytes, as compared with cells derived from the parental C57BL/6 (B6) mice, was correlated with increased levels of p53 protein and inhibition of p53-mediated transcription of target genes that encode proapoptotic proteins. Conversely, knockdown of p202 expression in B6.Nba2 cells resulted in stimulation of p53-mediated transcription. We found that p202 bound to p53 in the N-terminal region (aa 44-83) comprising the proline-rich region that is important for p53-mediated apoptosis. Consistent with the binding of p202 to p53, increased expression of p202 in B6.Nba2 mouse embryonic fibroblasts inhibited UV-induced apoptosis. Taken together, our observations support the idea that increased expression of p202 in B6.Nba2 mice increases the susceptibility to develop lupus, in part, by inhibiting p53-mediated apoptosis.
The Journal of Immunology 06/2006; 176(10):5863-70. DOI:10.4049/jimmunol.176.10.5863 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The majority of human prostate cancer cell lines, including the two "classical" cell lines DU-145 and PC-3, are reported to be androgen receptor (AR)-negative. However, other studies have provided evidence that the DU-145 and PC-3 cell lines express AR mRNA. These contradictory observations prompted us to investigate whether DU-145 and PC-3 cell lines express the androgen receptor. Using antipeptide antibodies directed against three distinct regions of the human AR protein and an improved method to detect AR protein in immunoblotting, we report that DU-145 and PC-3 cell lines express AR protein. We found that the relative levels of the AR mRNA and protein that were detected in DU-145 and PC-3 cell lines were lower than the LNCaP, an AR-positive cell line. Moreover, the antibody directed against the non-variant region (amino acids 299-315), but not the variant N- or C-terminal region (amino acids 1-20 and 900-919, respectively) of the human AR protein, detected the expression of AR in all prostate cancer cell lines. Notably, treatment of these cell lines with dihydrotestosterone (DHT) resulted in measurable increases in the AR protein levels and considerable nuclear accumulation. Although, treatment of DU-145 and PC-3 cells with DHT did not result in stimulation of the activity of an AR-responsive reporter, knockdown of AR expression in PC-3 cells resulted in decreases in p21(CIP1) protein levels, and a measurable decrease in the activity of the p21-luc-reporter. Our observations demonstrate the expression of AR protein in DU-145 and PC-3 prostate cancer cell lines.
[Show abstract][Hide abstract] ABSTRACT: Expression of androgen receptor (AR) in prostate epithelial cells is thought to regulate cell proliferation, differentiation, and survival. However, the molecular mechanisms remain unclear. We report that re-expression of AR in PC-3 human prostate cancer cell line resulted in upregulation of IFI16 protein, a negative regulator of cell growth. We found that the IFI16 protein bound to AR in a ligand-dependent manner and the DNA-binding domain (DBD) of the AR was sufficient to bind IFI16. Furthermore, re-expression of IFI16 protein in LNCaP prostate cancer cells, which do not express IFI16 protein, resulted in downregulation of AR expression and an inhibition of the expression of AR target genes. Our observations identify a role for IFI16 protein in AR-mediated functions.
[Show abstract][Hide abstract] ABSTRACT: Defects in interferon (IFN) signaling that result in loss of expression of IFN-inducible proteins are associated with cellular immortalization, an important early event in the development of human cancer. Here we report that loss of IFN-inducible IFI 16 expression in human fibroblasts allows bypass of cellular senescence. We found that levels of IFI 16 mRNA and protein were higher in human old versus young fibroblasts and immortalization of fibroblasts with telomerase resulted in decreased expression of IFI 16. Moreover, overexpression of IFI 16 in immortalized fibroblasts strongly inhibited cell proliferation. Interestingly, knockdown of IFI 16 expression in fibroblasts inhibited p53-mediated transcription, downregulated p21(WAF1) expression, and extended the proliferation potential. Importantly, treatment of immortal cell lines with 5-aza-2'-deoxycytidine, an inhibitor of DNA methyltransferase, resulted in upregulation of IFI 16. Our observations support the idea that increased levels of IFI 16 in older populations of human fibroblasts contribute to cellular senescence.
[Show abstract][Hide abstract] ABSTRACT: Systemic lupus erythematosus (SLE) is a prototype autoimmune disease. In human SLE patients, as well as in mouse models of SLE, the development of disease is associated with increased levels of pro-inflammatory cytokines, such as interleukin-6 (IL-6). However, IL-6 target genes contributing to the development of disease remain to be identified. Our previous studies of one mouse model of SLE identified an interferon-inducible gene, Ifi202, as a major contributor to the disease. We now report that IL-6 induces expression of the Ifi202 gene. We found that IL-6 treatment of mouse splenocytes increased levels of Ifi202 mRNA and p202 protein. Furthermore, IL-6 treatment of NIH 3T3 cells or expression of a constitutively active form of STAT3, a known mediator of IL-6 signaling, stimulated the activity of a 202-luc-reporter through a potential STAT3 DNA-binding site (the 202-SBS) present in the 5'-regulatory region of the Ifi202 gene. Moreover, treatment of cells with IL-6 stimulated binding of the transcription factor STAT3 to an oligonucleotide containing the 202-SBS in gel-mobility shift assays and to the 5'-regulatory region of the Ifi202 gene in chromatin immunoprecipitation assays. Importantly, site-directed mutagenesis of 202-SBS or expression of a dominant negative form of STAT3 significantly reduced constitutive as well as IL-6-stimulated activity of the 202-luc-reporter. Together, our observations support the idea that IL-6 stimulates transcription of the Ifi202 gene through STAT3 activation and predict that increased levels of IL-6 in lupus contribute to up-regulation of p202.
[Show abstract][Hide abstract] ABSTRACT: Increased expression of p202 (52 kDa), an interferon (IFN)-inducible murine protein, in splenic cells (B- and T-cells) derived from female mice of the lupus-prone strains is correlated with increased susceptibility to develop systemic lupus erythematosus. However, the molecular mechanisms remain unclear. Our previous studies have indicated that, in IFN-treated fibroblasts, p202 is detected both in the cytoplasm and in the nucleus. Moreover, in the cytoplasm, a fraction of p202 associates with a membranous organelle. Here we report that, in the cytoplasm, a fraction of p202 associated with mitochondria. Additionally, we found that the constitutive p202 is primarily detected in the cytoplasm. Remarkably, the IFN treatment of cells potentiated nuclear accumulation of p202. Our observations are consistent with the possibility that IFN signaling regulates p202 levels as well as its nucleocytoplasmic distribution. These observations will serve as a basis to elucidate the molecular mechanisms by which p202 contributes to lupus susceptibility.
[Show abstract][Hide abstract] ABSTRACT: Studies have indicated that ectopic expression of p202, an interferon (IFN)-inducible retinoblastoma (Rb)-binding protein, in cultured cells retards cell proliferation and modulates cell survival. Consistent with a role of p202 in cell cycle regulation, levels of p202 increase in cells arrested in the G0/G1 phase of cell cycle after withdrawal of serum growth factors. However, a role for p202 in cell growth arrest remains to be defined. Moreover, it remains unclear how levels of p202 are upregulated during the cell growth arrest. Here, we report that Rb upregulates expression of Ifi202 gene. We found that basal as well as IFN-induced levels of p202 were significantly higher in wild-type (Rb(+/+)) mouse embryonic fibroblasts (MEFs) than isogenic Rb(-/-) MEFs. Consistent with the regulation of Ifi202 gene by Rb, expression of functional Rb, but not a pocket mutant of it, stimulated the activity of a reporter whose expression was driven by the 5'-regulatory region of Ifi202 gene. Importantly, the stimulation by Rb was dependent, in part, on a JunD/AP-1 DNA-binding site present in the 5'-regulatory region of the Ifi202 gene. Moreover, basal levels of p202 were significantly higher in wild-type (JunD(+/+)) than isogenic JunD(-/-) MEFs. Additionally, we found that increased expression of p202 potentiated the Rb-mediated inhibition of cell growth and mutations in the Rb-binding motif (LxCxE) of p202 significantly reduced cell survival. Together, our observations support the idea that the transcriptional activation of Ifi202 gene by Rb/JunD may be important for the regulation of cell growth and survival.
[Show abstract][Hide abstract] ABSTRACT: Recent studies have implicated interferon signaling in the regulation of cellular senescence. However, the role of specific interferon-inducible proteins in cellular senescence remains to be defined. Here we report that IFI 16, an interferon-inducible transcriptional modulator from the p200-protein family, contributes to cellular senescence of prostate epithelial cells. Normal human prostate epithelial cells (PrEC) in culture expressed detectable levels of IFI 16, and the levels increased more than fourfold when cells approached cellular senescence. Consistent with a role of IFI 16 in cellular senescence, human prostate cancer cell lines either did not express IFI 16 or expressed a variant form, which was primarily detected in the cytoplasm of prostate cancer cells and not in the nucleus. Moreover, overexpression of functional IFI 16 in human prostate cancer cell lines inhibited colony formation. Additionally, ectopic expression of IFI 16 in clonal prostate cancer cell lines was associated with a senescence-like phenotype, production of senescence-associated beta-galactosidase (a biochemical marker for cellular senescence), and reduction of S-phase cells in culture. Importantly, upregulation of p21WAF1 and inhibition of E2F-stimulated transcription accompanied inhibition of cell growth by IFI 16 in prostate cancer cell lines. Collectively, our observations support the idea that increased levels of IFI 16 in PrECs contribute to senescence-associated irreversible cell growth arrest.
[Show abstract][Hide abstract] ABSTRACT: Previous studies have revealed that p202 (52 kDa), an interferon (IFN) and differentiation-inducible protein, negatively regulates cell proliferation and modulates cell survival. However, the role of p202 in transformed cells remains to be investigated. Here we report that constitutive expression of oncogenic H-Ras (Q61L) in NIH 3T3 cells, which resulted in cell transformation, was associated with increases in the steady-state levels of 202 RNA and protein. Interestingly, the increase in p202 levels in transformed cells correlated with increases in the activity of the transcription factor c-Jun/AP-1, which bound to the two potential AP-1 DNA binding sites (the AP-1CS1 and AP-1CS2) in the 5'-regulatory region of the 202 gene in gel mobility shift assays. Furthermore, the site-directed mutagenesis, coupled with promoter-reporter analyses, revealed that these two AP-1 DNA binding sites contribute to the regulation of the 202 gene in Ras transformed cells. Because treatment of transformed cells with a specific inhibitor of MEK (PD 98059) resulted in significant decreases in the levels of p202, these observations raise the possibility that in transformed cells Ras/Raf/MEK pathway regulates the transcriptional activation of the 202 gene. Significantly, decreases in the levels of p202 in Ras transformed NIH 3T3 cells under reduced serum conditions increased the susceptibility to apoptosis. Collectively, our observations support the idea that the transcriptional increases in the levels of p202 by oncogenic H-Ras in NIH 3T3 cells are needed for cell survival.