Changes in cAMP-dependent and Ca2(+)-phospholipid-dependent protein kinase activities in suspension cultures of porcine thyroid cells.

The morphological and functional characteristics and the activities of cyclic AMP- (PKA I and PKA II) and calcium and phospholipid-dependent (PKC) protein kinases were studied in 2-day-old suspension cultures of porcine thyroid cells and were compared with those in freshly dissociated cells and intact glands. Thyroid cell morphology changed during the 2-day culture in the absence of specific regulators. This is characterized by a loss of cellular polarity, exo- and endocytotic vesicles and membranes of the rough endoplasmic reticulum, and an increase in the number of lysosomes, pseudomyelinic structures, lipidic inclusions and free ribosomes. Functional changes are characterized by a progressive decrease in protein iodination and its sensitivity to TSH stimulation. The total PKA activity in the cytosols of these cultures was slightly greater than that of freshly prepared tissue, due to the selective and significant accumulation of PKA I in cultured cells. In the particulate fraction the PKA activity was unchanged. PKC is the major kinase activity in porcine thyroids, and remains so in cultured cells. The slight drop in its activity in cytosols was offset by a significant increase in the particulate fraction, suggesting an intracellular redistribution of this kinase in cultured cells. The PKC activity is also partly activated in both the cytosol and particulate fraction, which results in an increased basal activity. The changes in PKA and PKC activities greatly modified the PKC/PKA ratios in the cytosols and the particulate fractions of cultured cells. These modifications could be partly responsible for the changes in sensitivity of cultured cells to the agents which control their activity.