DIFFERENTIAL TYROSINE PHOSPHORYLATION ACTIVATION OF ONCOGENIC PROLINE-DIRECTED PROTEIN-KINASE F-A GSK-3-ALPHA IN WELL AND POORLY DIFFERENTIATED HUMAN PROSTATE CARCINOMA-CELLS/

Computer analysis of protein phosphorylation site sequences revealed t hat transcriptional factors and viral oncoproteins are prime targets f or regulation of proline-directed protein phosphorylation, suggesting an association of the proline-directed protein kinase (PDPK) family wi th neoplastic transformation and tumorigenesis. In this report, an imm unoprecipitate activity assay of proline-directed protein kinase F-A/g lycogen synthase kinase-3 alpha (PDPK F-A/GSK-3 alpha) has been optimi zed to demonstrate significantly increased (p < 0.01) activity in poor ly differentiated human prostate carcinoma PC-3 cells (55.5 +/- 3.8 un its/mg) when compared to well-differentiated LNCaP cells (28.1 +/- 2.3 units/mg). Immunoblotting analysis revealed that increased activity o f this PDPK in PC-3 cells is due not to overexpression of the protein, but to enhanced tyrosine phosphorylation of the kinase. When treated with genistein (a protein tyrosine kinase PTK inhibitor), the enhanced tyrosine phosphorylation/activation of the kinase in PC-3 cells can b e blocked. Conversely, when treated with vanadate (a protein tyrosine phosphatase PTP inhibitor), the phosphotyrosine content of PDPK F-A/GS K-3 alpha in LNCaP cells can be promoted to the level of PC-3 cells. I n sharp contrast, the PTK inhibitor has little effect on the tyrosine phosphorylation level of the kinase in LNCaP cells, whereas the PTP in hibitor has little effect on the tyrosine phosphorylation level of the kinase in PC-3 cells. Taken together, the results provide initial evi dence that the tyrosine phosphorylation/activation levels of this onco genic PDPK can be differentially regulated in well-and poorly differen tiated prostate carcinoma cells.