Proteomic-based analysis of nuclear signaling: PLCβ1 affects the expression of the splicing factor SRp20 in Friend erythroleukemia cells

An extensive body of evidence links inositide-specific phospholipase C (PLC) to the nucleus and the main isoform located in the nucleus is PLCβ₁. Constitutive overexpression of nuclear PLCβ₁ has been previously shown to inhibit Friend erythroleukemia cells differentiation and to induce cell cycle progression targeting cyclin D3. The aim of this study was to identify new proteins regulated by PLCβ₁ overexpression, given the role exerted by its signaling in the nucleus during cell growth and differentiation. To identify novel downstream effectors of nuclear PLCβ₁-dependent signaling in Friend erythroleukemia cells, we performed the high-resolution 2-DE-based proteomic analysis. Using a proteomic approach we found that SRp20, a member of the highly conserved SR family of splicing regulators, was down-regulated in cells overexpressing nuclear PLCβ₁ as compared with wild-type cells. Reduction in SRp20 was confirmed by 2-D Western blotting. Moreover, we have shown that nuclear PLCβ₁ is bound to the SRp20 splicing factor. Indeed, by immunoprecipitation and subcellular fractioning, we have demonstrated that endogenous PLCβ₁ and SRp20 physically interact in the nucleus. Here we show the existence of a PLCβ₁-specific target, the splicing factor SRp20, whose expression is specifically down-regulated by the nuclear signaling evoked by PLCβ₁.