摘要：

Phosphoinositide-specific phospholipase C (PLC) control the levels of their substrate phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), and its hydrolysis products diacylglycerol (DAG) and Ins(1,4,5)P3, second messengers key to growth control and cell movement. The former is modulated by breakdown of plasma membrane and nuclear phosphoinositides, while the latter is mediated by phosphoinositide-driven remodeling of the actin cytoskeleton. The roles of PLC in the etiology and progression of breast carcinoma, however, are poorly understood. Previous studies reported a correlation between PLCβ2 expression and breast tumor grade, making PLCβ2 a potential marker for clinical outcome (Bertagnolo et al., 2006). While over-expression of PLCβ2 is not sufficient to induce transformation of normal breast epithelial cells, it appears to play a role in promoting cell migration (Bertagnolo et al., 2007). Here we examined the expression of this and other PLC mRNA (β1-β4, δ1, δ3 and δ4, γ1 and γ2) in normal breast epithelial lines, MCF-10A, and compared that pattern to breast tumor lines MDA-MB-231 and to T47D, using real-time relative-quantification PCR. Our results show that PLCγ1, γ2 and δ1 and δ3 are more highly expressed in the transformed cell lines compared to MCF-10A when normalized to mRNA encoding various house keeping proteins; whereas PLCβ2 mRNA levels were considerably lower than other PLC subtypes, including PLCβ1 in the metastatic lines. Examination of PLC mRNA levels from normal and cancerous human breast tissue showed a similar pattern of expression, however, when staging or tumor size was considered, PLCδ1 and δ3 expression were positively correlated. To test whether PLCδ1 or δ3 played any role in tumor cell proliferation or cell migration, we transfected cells with siRNA specifically targeting these isoforms. RNAi mediated knockdown of either PLC isoform, reduced proliferation of the MDA-MB-231 cells. Morphological changes including cell rounding, and surface blebbing and nuclear fragmentation were observed. These changes were accompanied by reductions in cell migration activities. On the other hand, PLCδ1 knockdown failed to cause comparable morphological changes in the normal MCF-10A line, but did reduce cell proliferation and migration. Taken together, these data are consistent with the idea that PLCδ1 and δ3 isoforms support the growth and migration of normal and neoplastic mammary epithelial cells in vitro.

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