Protein kinase C d inhibits the secretion of proteolytic enzymes in murine mammary cells

ALEJANDRO J. URTREGER; VALERIA C. GROSSONI; MARCELO G. KAZANIETZ; ELISA D. BAL DE KIER JOFFÉ

Washington, EEUU.

Congreso; 97th Annual Meeting of the American Association for Cancer Research; 2006

American Association for Cancer Research (AACR)

PKC isozymes are serine-threonin kinases that control several cell functions, including proliferation, differentiation, malignant transformation, and metastatic dissemination. We have previously shown that overexpression of the novel calcium-independent protein kinase C d (PKCd) in normal murine mammary cells (NMuMG) was associated with increased proliferation and resistance to apoptosis induced by cytotoxic drugs or serum starvation. Moreover, PKCd overexpression led to anchorage-independent growth, a property closely related with the malignant phenotype. In the present work we investigated whether PKCd could modulate the production of proteolytic enzymes, such as urokinase (uPA) and metalloproteinase-9 (MMP-9), molecules directly associated with the metastatic dissemination process. Two methodologies were used: stable overexpression of PKCd and PKCd depletion using RNAi. NMuMG cells overexpressing PKCd showed a 67% reduction in the secretion of uPA compared to vector-transfected (control) cells, as well as a 63% reduction in MMP-9 secretion. Furthermore, treatment with the PKC activator PMA induced a dose-dependent inhibition of uPA production in NMuMG-PKCd cells (70% and 95% reduction for 25 and 50 nM PMA respectively). Similar results were observed for the secretion of MMP-9. The production of proteases was not significantly altered in control cells after PMA treatment. On the other hand, cells in which PKCd had been depleted using RNAi showed a marked increase (4-fold) in uPA levels as well as in MMP-9 secretion (8-fold). Our results demonstrate that PKCd has a negative modulatory role in the secretion of uPA and MMP-9 in normal murine mammary cells. Although our previous observations showed that PKCd was inducing changes compatible with a malignant phenotype, the present results strongly suggest that PKCd plays an important role in limiting metastatic dissemination by inhibiting the secretion of proteolytic enzymes that modulate invasiveness. In summary, PKCd seems to be playing multiple roles in the control of breast carcinogenesis.