Endogenous N-Terminal Truncated STAT5 Expressed from Alternative Start Codons Promotes SCF Signaling in Murine Primary Mast Cell Cultures.

摘要: Signal transducer and activator of transcription (STAT5) has important functions in hematopoiesis. Our prior work with mice which two coding exons STAT5a STAT5b have been deleted (STAT5ab−/−) shown that mast cells derived the presence interleukin(IL)-3 stem cell factor (SCF) severe defects survival proliferation (Shelburne et al. Blood102:1290; 2002). However, mechanism for STAT5 activation by SCF is unclear. In erythroid cells, not tyrosine phosphorylated alone. We set out to determine whether some SCF-induced could be rescued c-Kit+Fcγ+ primary bone marrow (BM) or fetal liver (FL) cultures from STAT5ab−/− mice. mouse had a normal chemotactic response compared wild-type however we found they highly expressed N-terminal truncated isoforms (STAT5ΔN) position 102 136. contrast, expression STAT5ΔN tissues such as spleen brain was barely detectable. While naturally occuring C-terminal variants bind DNA but do transactivate target genes, defective tetramerization. Generally, N-terminus STATs also believed essential function. Therefore, used test mutants (STAT5ΔN1–136 STAT5W37A) functionally restore previously reported vitro. Both were dimerization-competent tetramerization-deficient. MSCV-based retroviral vectors expressing these upstream IRES-GFP stably transduced into cells. A strong selective advantage GFP+ observed all containing STAT5wt, STAT5ΔN, STAT5W37A control. Inversely, only mutant conferred advantage, suggesting heterodimer (ΔN/wt) between STAT5wt most active. apoptosis experiments, protected following cytokine withdrawal. homodimer (ΔN/ΔN) intermediate terms growth reconstitution potential than heterodimer. overexpression above endogenous alone sufficient correct defects. To further explore role obtained FL-derived new STAT5null/null where entire STAT5ab locus using Cre-LoxP system (Cui MCB, press). These lacked STAT5ΔN. Unlike showed 9-fold reduction chemotaxis relative controls. Importantly, completely gene transfer (P=0.018) (P=0.02) IRGFP 1) active different degree depending on specific function type 2) co-expression along full-length confers maximal SCF-mediated responsiveness This uncovers STAT5-mediated responses are regulated via formation functional heterodimers.