The
protein kinase C (PKC) family has been functionally linked to
cancer. It has been suggested that atypical
PKCs contribute to cell proliferation and
cancer progression. With respect to
breast cancer, PKCζ has been found to play a key role in intracellular transduction of mitogenic and apoptotic signals using mammary cell lines. However, little is known about its function in vivo. Here we examined the correlation between PKCζ
protein levels and important clinicopathologic factors in
breast cancer using patient samples. To conduct the study, 30 invasive
ductal carcinoma cases and their paired normal tissues were used for tissue microarray analysis (TMA) and 16 were used for western blot analysis. In addition, the correlation between PKCζ expression levels and clinicopathologic characteristics was determined in 176 cases with relevant clinical data. Finally, the correlation between PKCζ and epithelial
growth factor receptor 2 (HER2) expressions was determined using three
breast cancer cell lines by western blot analysis. Both TMA and western blot results showed that PKCζ
protein was highly expressed in primary
tumors but not in paired normal tissue. The correlation study indicated that high PKCζ levels were associated with premenopausal patients (p = 0.019) and worse prognostic factors, such as advanced clinical stage, more lymph node involvement and larger
tumor size. Both disease-free survival and overall survival rates were lower in the high PKCζ group than those in the low PKCζ group. No correlation was observed between PKCζ levels and age, histological grade, or
estrogen or
progesterone receptor expression status. A positive correlation between PKCζ and HER2 levels was observed in both
tumor samples and cell lines. Our observations link PKCζ expression with factors pointing to worse prognosis, higher HER2 levels and a lower survival rate. This suggests that PKCζ
protein levels may serve as a prognostic marker of
breast cancer.