Intestinal cell kinase, a MAP kinase-related kinase, regulates proliferation and G1 cell cycle progression of intestinal epithelial cells.
Intestinal cell kinase (ICK), originally cloned from the intestine and expressed in the intestinal crypt epithelium, is a highly conserved serine/threonine protein kinase that is similar to mitogen-activated protein kinases (MAPKs) in the catalytic domain and requires dual phosphorylation within a MAPK-like TDY motif for full activation. Despite these similarities to MAPKs, the biological functions of ICK remain unknown. In this study, we report that suppression of ICK expression in cultured intestinal epithelial cells by short hairpin RNA (shRNA) interference significantly impaired cellular proliferation and induced features of gene expression characteristic of colonic or enterocytic differentiation. Downregulation of ICK altered expression of cell cycle regulators (cyclin D1, c-Myc, and p21(Cip1/WAF1)) of G(1)-S transition, consistent with the G(1) cell cycle delay induced by ICK shRNA. ICK deficiency also led to a significant decrease in the expression and/or activity of p70 ribosomal protein S6 kinase (S6K1) and eukaryotic initiation factor 4E (eIF4E), concomitant with reduced expression of their upstream regulators, the mammalian target of rapamycin (mTOR) and the regulatory associated protein of mTOR (Raptor). Furthermore, ICK interacts with the mTOR/Raptor complex in vivo and phosphorylates Raptor in vitro. These results suggest that disrupting ICK function may downregulate protein translation of specific downstream targets of eIF4E and S6K1 such as cyclin D1 and c-Myc through the mTOR/Raptor signaling pathway. Taken together, our findings demonstrate an important role for ICK in proliferation and differentiation of intestinal epithelial cells.
Fu
Zheng
Z
Digestive Health Center of Excellence, Univ. of Virginia Health System, PO Box 800708, Charlottesville, VA 22908, USA. zf6n@virginia.edu
Kim
Jungeun
J
Vidrich
Alda
A
Sturgill
Thomas W
TW
Cohn
Steven M
SM
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D018938:Caco-2 Cells; D002454:Cell Differentiation / Q000235:genetics*; D049109:Cell Proliferation; D019938:Cyclin D1 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004847:Epithelial Cells / Q000201:enzymology* / Q000473:pathology; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D016193:G1 Phase; D005786:Gene Expression Regulation; D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology* / Q000473:pathology; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011506:Proteins; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D034622:RNA Interference; D000076223:Regulatory-Associated Protein of mTOR; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
D048868:Adaptor Proteins, Signal Transducing; C530104:CCND1 protein, human; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D039561:Eukaryotic Initiation Factor-4E; D047908:Intracellular Signaling Peptides and Proteins; C489427:MYC protein, human; D046912:Multiprotein Complexes; D011506:Proteins; D016271:Proto-Oncogene Proteins c-myc; C463659:RPTOR protein, human; D000076223:Regulatory-Associated Protein of mTOR; D014157:Transcription Factors; D019938:Cyclin D1; C097276:CILK1 protein, human; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1
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