Expression of cellular oncogenes in the myocardium during the developmental stage and pressure-overloaded hypertrophy of the rat heart.

Proto-oncogenes have been revealed to participate in normal cell proliferation as well as in cell transformation. Since cardiac myocytes are terminally differentiated, they cannot divide except in the fetal period. To determine the role of cellular oncogenes in the growth of the heart, the expression pattern of eight cellular oncogenes during the developmental stage and pressure-overloaded hypertrophy of the rat hearts were examined in vivo. Northern blot analysis was performed with eight oncogene probes (myc, fos, Ha-ras, src, erbA, erbB, sis, myb). Pressure overload increased the levels of cellular (c-) fos, c-myc, and c-Ha-ras. An increase of c-fos and c-myc was detected at 30 minutes and 2 hours, respectively; the levels peaked at 8 hours, and they returned to baseline by 48 hours after aortic constriction. However, the level of c-Ha-ras showed a gradual increase. During the course of development, the expression of c-myc was detectable only in the embryonic stage, whereas the expression of c-fos was not detected in the fetal period, was increased after birth, and peaked in 200-day-old adults. The expression of c-Ha-ras was almost the same throughout the development. Cellular oncogenes were expressed in the heart in response to pressure overload and in a stage-specific manner. These results suggest that cellular oncogenes may participate in the normal developmental process and hypertrophy of hearts and that the cellular hypertrophy induced by pressure overload may share a similar mechanistic pathway with cell proliferation.