Extracellular Signal-regulated Kinases (ERKs) Phosphorylate Lin28a Protein to Modulate P19 Cell Proliferation and Differentiation
A research team led by Dr. Daming Gao, at Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences (CAS), recently revealed a new regulatory mechanism connecting extra-cellular signal and micro-RNA function. This study was just published in Journal of Biological Chemistry
Proliferation and differentiation are usually tightly coupled processes for stem cells which are regulated by signals from extracellular environment. Among these signals, MAPK-ERK signaling pathway plays an important role in controlling cell proliferation in most somatic cells by facilitating the transition through early G1 phase of the cell cycle. Activation or prolongation of MAPK signaling often induces differentiation, then connects cell proliferation and development events. Lin28a, originally discovered in the nematode Caenorhabditis elegans and highly conserved across species, is implicated in cell proliferation and pluripotency control. By directly binding to its target RNAs, Lin28a is known to inhibit maturation of let-7 miRNA family and promotes their turnover, thereby influencing an army of let-7 targets including c-Myc, Ras, and cyclin D1, as well as Lin28a itself, which are master regulators of cell proliferation and the pluripotent status of stem cells. By editing lin28a gene with the CRISPR/Cas9-based method, P19 mouse embryonic carcinoma(EC) stem cells expressing Lin28a-S200A (phospho-deficient) and Lin28a-S200D (phospho-mimetic) mutants were generated to study the functional impact of Ser-200 phosphorylation. Lin28a-S200D-expressing cells, but not Lin28a-S200A-expressing or control P19 EC stem cells, displayed impaired inhibition of let-7 miRNA, whereas Lin28a-S200A knock-in cells expressed less let-7 miRNA, proliferated faster, and exhibited differentiation defect upon retinoic acid induction. Further studies showed that phosphorylation of Lin28a at Ser200 modulated differentiation and proliferation of P19 EC stem cells by decreasing cyclin D1 via let-7 dependent mechanism. Then decreased cyclin D1 decelerated cell proliferation and facilitated the escape from self-renewal cycle to start the differentiation process. This work shed new light on how Lin28a function is modulated at the posttranslational level and thereby responds to major signaling pathways.
This work got great help from Prof. Wu Ligang (Institute of Biochemistry and Cell Biology, SIBS, CAS), Prof. Chen Lingling ( Institute of Biochemistry and Cell Biology, SIBS, CAS) and Prof. Zhou Hu (Shanghai Institute of Materia Medica, CAS). The study was supported by the grants from the Ministry of Science and Technology of China and the National Natural Science Foundation of China.
Reference:
http://www.jbc.org/content/early/2017/02/08/jbc.C117.775122.abstract
AUTHOR CONTACT:
Gao Daming, Ph.D.
Shanghai Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences,
Chinese Academy of Sciences, Shanghai, China
Tel: +86-21-54921281;
E-mail: dgao@sibcb.ac.cn 
Legend: ERK mediated Ser-200 phosphorylation modulated differentiation and proliferation of P19 EC stem cells by decreasing cyclin D1 via let-7 dependent mechanism. (Image provided by Prof. Gao Daming’s lab)
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