LOCALIZATION OF PROTEIN-KINASE-C ISOZYMES IN RAT COLON

We have demonstrated previously the presence of classical (alpha), nov el (delta and epsilon), and atypical (zeta) protein kinase C (PKC) iso zymes in human and rat colonic mucosa (L. A. Davidson et al., Arch. Bi ochem. Biophys., 312: 547-553, 1994). To gain insight into the functio ns of individual PKC isozymes in colonic epithelium in situ, we determ ined the localization of the major PKC isozymes expressed in normal ra t colonic epithelial cells using in situ reverse transcription (RT)-PC R and immunohistochemistry (IH). Cytokeratin, a positive biological co ntrol known to be expressed in epithelial cells, was shown by in situ RT-PCR and IH to be expressed only in epithelial cells within the colo nic crypt. PKC gamma, a negative control for the colon since it is exp ressed only in the central nervous system, was not detectable in colon sections by either methodology. In situ RT-PCR analysis revealed that PKC alpha, delta, epsilon, and zeta mRNAs are expressed in epithelial cells along the entire colonic crypt. In addition, PKC delta and zeta mRNA are expressed in the stromal layer. All four PKC isozymes in the colonic epithelial cells were also detected by IH. However, in genera l, isozyme protein expression was greater at the top of the crypt axis , associated primarily with cells having acquired a differentiated phe notype. These results suggest that PKC isozyme protein expression may be localized to mature differentiated cells at the top of the colonic crypt. Therefore, PKC isozyme-dependent signal transduction may play a role in colonic epithelial cell ontogeny along the colonic crypt axis .