Effect of proline rich domain of an RNA-binding protein Sam68 in cell growth process, death and B cell signal transduction.
BACKGROUND
Sam68 plays an important role as a multiple functional RNA binding nuclear protein in cell cycle progress, RNA usage, signal transduction, and tyrosine phosphorylation by Src during mitosis. However, its precise impact on these essential cellular functions remains unclear. The purpose of this study is to further elucidate Sam68 functions in RNA metabolism, signal transduction regulation of cell growth and cell proliferation in DT40 cell line.


METHODS
By using gene targeting method, we isolated a mutation form of Sam68 in DT40 cells and described its effect on cell growth process and signal transduction. Southern, Northern, and Western blot, phosphorylation and flow-cytometric analyses were performed to investigate the Sam68 functions.


RESULTS
A slower growth rate (2.1 hours growth elongation) and longer S phase (1.7 hours elongation) was observed in the Sam68 mutant cells. Serum depletion resulted in increased amounts of dead cells, and expansion of S phase in mutant cells. Upon B cell cross-linking, the maximal level of tyrosine phosphorylation on BLNK was observed to be significantly lower in mutant cells.


CONCLUSIONS
The proline rich domain of Sam68 is involved in cell growth control by modulating the function of mRNAs in S phase or earlier and the functions as an adaptor molecule in B cell signal transduction pathways.
Li
Qing-hua
QH
State Key Laboratory of Experimental Hematology, Institute of Hematology & Hospital of Blood Diseases, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin 300020, China.
Fan
Tian-xue
TX
Pang
Tian-xiang
TX
Yuan
Wen-su
WS
Han
Zhong-chao
ZC
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000502:physiology*; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002453:Cell Cycle / Q000502:physiology; D016923:Cell Death / Q000502:physiology; D048708:Cell Growth Processes / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D011392:Proline / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D011947:Receptors, Antigen, B-Cell / Q000276:immunology / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D016895:Culture Media, Serum-Free; D016601:RNA-Binding Proteins; D011947:Receptors, Antigen, B-Cell; D014443:Tyrosine; D011392:Proline