The mRNA of L-type calcium channel elevated in colon cancer - Protein distribution in normal and cancerous colon

Previous reports indicate that the mRNA for the cardiac isoform of the volt age-gated L-type calcium channel (alpha 1C) is elevated in colon cancer, Th e aim of these experiments was to verify that the mRNA for alpha 1C was sig nificantly Increased in tumors of two separate populations of patients when compared to normal adjacent mucosa, The second aim was to measure the dist ribution of alpha (1C1) using immunocytochemistry in normal human colon and in colon cancer and to determine what might regulate the channel expressio n. biopsies were taken horn patients with various stages of colon cancer an d nearby normal mucosa were used as control. RNA was prepared and mRNA leve l measured by semiquantitative reverse transcriptase-polymerase chain react ion, The mRNA of the calcium channel was compared with other markers includ ing beta -actin. The mRNA for alpha (1C) was increased significantly in col on cancers compared, to nearby adjacent mucosa, Using confocal microscopy a lpha (1C) was localized mainly at the apical membrane in the surface epithe lium of normal human colon with less distribution on the lateral and basal membranes. The channel was localized on the lateral and basal membranes in crypt cells, Calcium channel localization appeared to be nearer nuclei in c olon cancer samples, in part because of the smaller size of the cells. Like wise, cultured Caco-2 and T84 cells showed a membrane distribution, Western blotting indicated that a,, protein was Increased in nonconfluent cultures of colonic carcinoma cells compared to confluent cells and immunocytochemi stry confirms that there is more calcium channel protein in cells that are nonconfluent. We conclude that the increase in mRNA of a, subunit of the ca rdiac isoform of the L-type calcium channel may be a useful marker of colon cancer compared to other markers because the increase is large and this in crease can be documented on small samples using a simple semiquantitative r everse transcriptase-polymerase chain reaction. We found that alpha (1C) pr otein is increased when colonic cells are nonconfluent or dividing which ma y account for the increase in cancer.