Lin28 is a conserved cytoplasmic protein with an unusual pairing of RNA-binding motifs: a cold shock domain and a pair of retroviral-type CCHC zinc fingers. In the nematode C. elegans, it is a regulator of developmental timing. In mammals, it is abundant in diverse types of undifferentiated cells. However, its molecular function is unknown. In pluripotent mammalian cells, Lin28 is observed in RNase-sensitive complexes with poly(A)-binding protein, and in polysomal fractions of sucrose gradients, suggesting it is associated with translating mRNAs. Upon cellular stress, Lin28 locates to stress granules, which contain non-translating mRNA complexes. However, Lin28 also localizes to cytoplasmic processing bodies, or P-bodies, sites of mRNA degradation and microRNA regulation, consistent with it acting to regulate mRNA translation or stability. Mutational analysis shows that Lin28's conserved RNA binding domains cooperate to put Lin28 in mRNPs, but that only the CCHC domain is required for localization to P-bodies. When both RNA-binding domains are mutated, Lin28 accumulates in the nucleus, suggesting that it normally shuttles from nucleus to cytoplasm bound to RNA. These studies are consistent with a model in which Lin28 binds mRNAs in the nucleus and accompanies them to ribosomes and P-bodies. We propose that Lin28 influences the translation or stability of specific mRNAs during differentiation.
"In a previous study, we localized L1TD1 in the cytoplasmic processing bodies (P-bodies) based on its co-location with AGO2 and LIN28 (Närvä et al., 2012). However, both of these proteins are able to traffic between the cytoplasm and nucleus (Balzer and Moss, 2007; Robb et al., 2005). In addition, a recent MS analysis identified L1TD1 in the nuclear fraction (Sarkar et al., 2012). "
"c o m / l o c a t e / b b a m c r 4T-1. FLAG-mtLin28 (W46A, F55A & F73A in CSD and H147A & H169A in CCHC ZF domain) and two deletions, FLAG-Lin28-CSD and FLAG- Lin28-CCHC, were constructed as described . pCX-FLAG-PCAF was a gift from Dr. Hua Lu (Oregon Health & Science University). "
[Show abstract][Hide abstract] ABSTRACT: Lin28 is a small RNA-binding protein that plays an important role in regulating developmental timing, stem cell reprogramming, and oncogenesis. However, the significance of the effect of post-translational modifications on Lin28 activity is not fully understood. In this study, we demonstrated that PCAF directly interacted with and acetylated Lin28. We also showed that the acetylation of Lin28 can be specifically reversed by the deacetylase SIRT1. These findings suggest that the PCAF/SIRT1 balance plays an important role in regulating Lin28 activity. Furthermore, we found that the cold shock domain of Lin28 is the major target of PCAF-mediated acetylation, which leads to a severe reduction in the Lin28 protein levels and an increase in the level of mature let-7a. This study provides the first demonstration that post-translational modification regulates Lin28 activity during let-7a biogenesis and sheds light on the regulation of Lin28 in ES cells and carcinogenesis.
Biochimica et Biophysica Acta (BBA) - Molecular Cell Research 06/2014; 1843(6). DOI:10.1016/j.bbamcr.2014.03.001 · 5.02 Impact Factor
"The majority of the transcripts decreasing in both LIN28 association and translational efficiency include those in known LIN28-regulated pathways such as cell cycle and RNA metabolism (9,21). Downregulation of LIN28 has been shown to be important in hESC differentiation (51). "
[Show abstract][Hide abstract] ABSTRACT: LIN28 function is fundamental to the activity and behavior of human embryonic stem cells (hESCs) and induced pluripotent stem
cells. Its main roles in these cell types are the regulation of translational efficiency and let-7 miRNA maturation. However, LIN28-associated mRNA cargo shifting and resultant regulation of translational efficiency upon
the initiation of differentiation remain unknown. An RNA-immunoprecipitation and microarray analysis protocol, eRIP, that
has high specificity and sensitivity was developed to test endogenous LIN28-associated mRNA cargo shifting. A combined eRIP
and polysome analysis of early stage differentiation of hESCs with two distinct differentiation cues revealed close similarities
between the dynamics of LIN28 association and translational modulation of genes involved in the Wnt signaling, cell cycle,
RNA metabolism and proteasomal pathways. Our data demonstrate that change in translational efficiency is a major contributor
to early stages of differentiation of hESCs, in which LIN28 plays a central role. This implies that eRIP analysis of LIN28-associated
RNA cargoes may be used for rapid functional quality control of pluripotent stem cells under manufacture for therapeutic applications.
Nucleic Acids Research 05/2014; 42(12). DOI:10.1093/nar/gku430 · 9.11 Impact Factor
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