Protein Kinases D2 and D3 Are Novel Growth Regulators in HCC1806 Triple-negative Breast Cancer Cells.
ABSTRACT Aim: The role of protein kinase D (PKD) in the context of breast cancer cell biology is not clear.
The expression of PKD isoforms was assessed in various breast cancer cell lines and PKD isoform-specific siRNAs and selective inhibitors were used to study the role of PKD in breast cancer cell growth.
PKD2 and PKD3 were two major isoforms expressed at the highest levels in tumorgenic HCC1806 triple-negative breast cancer cells. Silencing PKD2 or PKD3 significantly inhibited HCC1806 cell proliferation, and PKD3 silencing had a higher inhibitory effect than PKD2 silencing on cell growth and PKD-mediated signaling. HCC1806 breast cancer cells were highly responsive to PKD inhibitors but not to a general protein kinase C (PKC) inhibitor.
We have identified PKD2 and PKD3, especially PKD3, as novel cell growth regulators in HCC1806 triple-negative breast cancer cells. Targeting PKD instead of all PKCs effectively inhibited cell proliferation in a number of breast cancer cell lines.
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ABSTRACT: PKD is a family of three serine/threonine kinases (PKD-1, -2 and -3) involved in the regulation of diverse biological processes including proliferation, migration, secretion and cell survival. We have previously shown that despite expression of all three isoforms in mouse epidermis, PKD1 plays a unique and critical role in wound healing, phorbol ester-induced hyperplasia and tumor development. In translating our findings to the human, we discovered that PKD1 is not expressed in human keratinocytes (KCs) and there is a divergence in the expression and function of other PKD isoforms. Contrary to mouse KCs, treatment of cultured human KCs with pharmacological inhibitors of PKDs resulted in growth arrest. We found that PKD2 and PKD3 are expressed differentially in proliferating and differentiating human KCs, with the former uniformly present in both compartments whereas the latter is predominantly expressed in the proliferating compartment. Knockdown of individual PKD isoforms in human KCs revealed contrasting growth regulatory roles for PKD2 and PKD3. Loss of PKD2 enhanced KC proliferative potential while loss of PKD3 resulted in a progressive proliferation defect, loss of clonogenicity and diminished tissue regenerative ability. This proliferation defect was correlated with upregulation of CDK4/6 inhibitor p15INK4B and induction of a p53-independent G1 cell cycle arrest. Simultaneous silencing of PKD isoforms resulted in a more pronounced proliferation defect consistent with a predominant role for PKD3 in proliferating KCs. These data underline the importance and complexity of PKD signaling in human epidermis and suggests a central role for PKD3 signaling in maintaining human epidermal homeostasis. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.Journal of Biological Chemistry 03/2015; 290(17). DOI:10.1074/jbc.M115.643742 · 4.60 Impact Factor
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ABSTRACT: Success of chemotherapy is generally impaired by multidrug resistance, intrinsic resistance, or acquired resistance to functionally and structurally irrelevant drugs. Multidrug resistance emerges via distinct mechanisms: increased drug export, decreased drug internalization, dysfunctional apoptotic machinery, increased DNA damage repair, altered cell cycle regulation, and increased drug detoxification. Several reports demonstrated that multidrug resistance is a multifaceted problem such that multidrug resistance correlates with increased aggressiveness and metastatic potential. Here, we tested the involvement of protein kinase D2, a serine/threonine kinase that was previously implicated in proliferation, drug resistance, and motility in doxorubicin-resistant MCF7 (MCF7/DOX) cell line, which served as an in vitro model for drug resistance and invasiveness. We showed that basal level activity of protein kinase D2 (PKD2) was higher in MCF7/DOX cells than parental MCF7 cells. To elucidate the roles of PKD2 MCF7/DOX, PKD2 expression was reduced via small interfering RNA (siRNA)-mediated knockdown. Results showed that acquired resistance of MCF7/DOX to doxorubicin was not affected by PKD2 silencing, while motility of MCF7/DOX cells was reduced. The results implied that PKD2 silencing might inhibit migration of MCF7/DOX cells without affecting chemoresistance significantly.Tumor Biology 01/2015; DOI:10.1007/s13277-015-3081-3 · 2.84 Impact Factor
- Tumor Biology 01/2015; · 2.84 Impact Factor