Protein kinase C and a viral K-RAS protein cooperatively enhance the response of adenylate cyclase to stimulators

Phorbol esters affect cyclic nucleotide-mediated responses in cultured chick lens annular pad cells

Cultured chick lens annular pad cells were treated with a lipid soluble cAMP analog, the phorbol ester TPA or a combination of the two compounds in order to assess their effects on mitotic activity, cell spreading and the accumulation of differentiation marker proteins. Both 8b-cAMP and TPA were individually able to inhibit mitotic activity in cells cultured in the presence of 5% serum. The combination of the two produced a greater degree of mitotic inhibition. Both compounds were also able to inhibit cellular spreading onto laminin coated surfaces. Opposite effects on the accumulation of differentiation marker proteins were observed for the two compounds. While 8b-cAMP increased levels of marker proteins, TPA or the combination of TPA and 8b-cAMP reduced levels of marker proteins. These data indicate that crosstalk between two distinct signal transduction systems in the lens is able to influence cell behaviors implicated in the development of secondary or posterior subcapsular cataract. In addition, these data demonstrate that both positive and negative regulatory influences affect the accumulation of differentiated characteristics.

C-terminal fragment of parathyroid hormone-related protein, PTHrP-(107-111), stimulates membrane-associated protein kinase C activity and modulates the proliferation of human and murine skin keratinocytes

Low concentrations of the C-terminal parathyroid hormone-related protein (PTHrP) fragments, PTHrP-(107-111) and PTHrP-(107-139), stimulated membrane-associated protein kinase Cs (PKCs), but not adenylyl cyclase or an internal Ca2+ surge, in early passage human skin keratinocytes and BALB/MK-2 murine skin keratinocytes. The fragment maximally stimulated membrane-associated PKCs in BALB/MK-2 cells at 5 x 10(-9) to 10(-8) M. The maximally PKC-stimulating concentrations of PTHrP-(107-111) also stopped or stimulated BALB/MK-2 keratinocyte proliferation depending on whether the cells were, respectively, cycling or quiescent at the time of exposure. Thus, just one brief (30-minute) pulse of 10(-8) M PTHrP-(107-111) stopped the proliferation of BALB/MK-2 keratinocytes for at least 5 days. On the other hand, daily 30-minute pulses of 10(-8) M PTHrP-(107-111) started and then maintained the proliferation of initially quiescent BALB/MK-2 cells. Similarly PTHrP-(107-111) inhibited DNA synthesis by cycling primary adult human keratinocytes, but it stimulated DNA synthesis by quiescent human keratinocytes.

Further definition of the protein kinase C activation domain of the parathyroid hormone

The protein kinase C (PKC) activation domain of the parathyroid hormone (PTH) was believed to be the 28-34 region of the molecule. We have now shown that PTH-(29-32) is the smallest PTH fragment that can stimulate significantly membrane-associated PKC activity in ROS 17/2 rat osteosarcoma cells. As was previously shown for full-length PTH-(1-84) and the fully bioactive PTH-(1-34) fragment, there were two peaks in the PKC response to PTH-(29-32): one peak was obtained with low picomolar concentrations and the other with much higher nanomolar concentrations of the fragment. The PKC-activating ability was unaffected by the loss of Asn33 and Phe34, but it was abolished by removing His32. Thus, the PTH-(28-31) and PTH-(29-31) fragments did not stimulate membrane-associated PKC activity. The much larger PTH-(1-31) fragment also did not stimulate membrane-associated PKC activity, although it stimulated adenylyl cyclase as strongly as PTH-(1-34). This functional sensitivity to the loss of the polar His32 was not caused by a specific need for His or another polar amino acid in this position because replacing it with the apolar Leu did not abolish adenylyl cyclase or PKC activation. It is concluded that the minimum, fully functional PKC activation domain of the PTH molecule is Gln29-Asp30-Val31-His32.

Transcription induction of c-Ki-ras with the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in normal and transformed liver cells

Results from nuclear run-off assays show that exposure of hepatocytes and Reuber H35B hepatoma cells to the tumour promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), leads to enhanced transcription of c-Ki-ras gene. This increase in transcription in turn results in an accumulation of the functionally active c-Ki-ras message. The half life of c-Ki-ras message in both normal and transformed livers cells is not altered by TPA and is determined to be 3.5 hr. The induction of c-Ki-ras message is accompanied by an increase in the level of c-Ki-ras protein.

Expression of c-Ki-ras in developing rat liver

1. Two major c-Ki-ras transcripts are present in rat liver throughout development. 2. Both transcripts are functional, i.e. translatable into ras protein. 3. They exhibit low levels in early foetuses and increase gradually towards term. 4. Peak levels of transcripts are detected on the fourth day of postnatal life. 5. Results from nuclear run-off assays demonstrate that the rise in level of transcripts is a result of increase in rate of transcription with the highest rate detected on the fourth day of postnatal life. 6. Western blot analysis reveals that the accumulation of c-Ki-ras protein clearly follows the pattern of changes in transcription of c-Ki-ras gene.

Parathyroid hormone stimulates protein kinase C but not adenylate cyclase in mouse epidermal keratinocytes

Intact human parathyroid hormone, hPTH [1-84], and the hPTH [1-34] fragment stimulated membrane-associated protein kinase C (PKC) activity in immortalized (but still differentiation-competent) murine BALB/MK-2 skin keratinocytes. Unexpectedly, the hormone and its fragment did not stimulate adenylate cyclase. The failure of PTH to stimulate adenylate cyclase activity was not due to the lack of a functioning receptor-cyclase coupling mechanism because the cells were stimulated to synthesize cyclic adenosine monophosphate (cyclic AMP) by the beta-adrenergic drug isoproterenol. Thus, skin keratinocytes seem to have an unconventional PTH receptor that is coupled to a PKC-activating mechanism but not to adenylate cyclase. These observations suggest that normal and neoplastic skin keratinocytes respond to the PTH-related peptide that they make and secrete.