Overexpression of PKC[alpha] is required to impart estradiol inhibition and tamoxifen-resistance in a T47D human breast cancer tumor model

• Published in: Carcinogenesis (New York) Vol. 27; no. 8; p. 1538
• Main Authors: Lin, Xin, Yu, Yanni, Zhao, Huiping, Zhang, Yiyun, Manela, Jessica, Tonetti, Debra A
• Format: Journal Article
• Language: English
• Published: Oxford Oxford Publishing Limited (England) 01.08.2006
• ISSN: 0143-3334; 1460-2180

We previously reported that stable overexpression of protein kinase C alpha (PKCα) in hormone responsive T47D:A18 breast cancer cells produces a hormone-independent/tamoxifen (TAM)-resistant and 17β-estradiol (E2)-inhibitory phenotype in vivo. Furthermore, overexpression of PKCα in T47D:A18 cells also results in cross-upregulation of PKCs β and δ. In this study, we further characterized the contribution of PKC isozymes α, β and δ to this complex phenotype. To determine whether downregulation of PKCα is sufficient to restore the hormone-dependent phenotype in T47D:A18/PKCα cells, PKCα was selectively knocked down using short hairpin RNA (shRNA). To determine the contribution of PKCβ or δ to the hormone-independent/TAM-resistant and E2-inhibitory phenotype, stable T47D:A18/PKCβ and T47D:A18/PKCδ clones were established. Downregulation of PKCα by shRNA in T47D:A18/PKCα20 cells also resulted in reduced PKCβ protein expression in vitro. Tumors established from a T47D:A18/PKCα/shRNA stable clone exhibit 50% reduction of PKCα protein without concomitant reduction in PKCβ, and exhibit partial reversal of the TAM-resistant and E2-inhibitory phenotype in vivo. Furthermore, stable overexpression of neither PKCβ nor PKCδ in T47D:A18 cells are sufficient to produce hormone-independent growth in vitro or in vivo, nor TAM-resistant and E2-inhibited growth in vivo. Taken together, these results suggest that PKCα is required to impart the TAM-resistant and E2-inhibitory phenotype in vivo.