Localization of protein kinase C isozymes in rat colon

We have demonstrated previously the presence of classical (alpha), novel (delta and epsilon), and atypical (zeta) protein kinase C (PKC) isozymes in human and rat colonic mucosa (L. A. Davidson et al., Arch. Biochem. Biophys., 312:547-553, 1994). To gain insight into the functions of individual PKC isozymes in colonic epithelium in situ, we determined the localization of the major PKC isozymes expressed in normal rat colonic epithelial cells using in situ reverse transcription (RT)-PCR and immunohistochemistry (IH). Cytokeratin, a positive biological control 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 colonic crypt. PKC gamma, a negative control for the colon since it is expressed 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 general, isozyme protein expression was greater at the top of the crypt axis, associated primarily with cells having acquired a differentiated phenotype. 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.