Protein kinase C βII and PKCι/λ: Collaborating partners in colon cancer promotion and progression

We previously showed that elevated expression of either protein kinase CβII (PKCβII) or PKCι/λ enhances colon carcinogenesis in mice. Here, we use novel bitransgenic mice to determine the relative importance of PKCβII and PKCι/λ in colon carcinogenesis in two complimentary models of colon cancer in vivo. Bitransgenic mice overexpressing PKCβII and constitutively active PKCι (PKCβII/caPKCι) or kinase-deficient, dominant-negative PKCι (PKCβII/kdPKCι) in the colon exhibit a similar increase in colon tumor incidence, tumor size, and tumor burden in response to azoxymethane (AOM) when compared with nontransgenic littermates. However, PKCβII/kdPKCι mice develop predominantly benign colonic adenomas, whereas PKCβII/caPKCι mice develop malignant carcinomas. In contrast, PKCβ-deficient (PKCβ^-/-) mice fail to develop tumors even in the presence of caPKCι. Our previous data indicated that PKCβII drives tumorigenesis and proliferation by activating β-catenin/Apc signaling. Consistent with this conclusion, genetic deletion of PKCβ has no effect on spontaneous tumorigenesis in Apc^min/+ mice. In contrast, tissue-specific knockout of PKCλ significantly suppresses intestinal tumor formation in Apc^min/+ mice. Our data show that PKCβII and PKCι/λ serve distinct, nonoverlapping functions in colon carcinogenesis. PKCβII is required for AOM-induced tumorigenesis but is dispensable for tumor formation in Apc^Min/+ mice. PKCι/λ promotes tumor progression in both AOM- and Apc ^min/+-induced tumorigenesis. Thus, PKCβII and PKCι, whose expression is elevated in both rodent and human colon tumors, collaborate to drive colon tumor formation and progression, respectively.