Up-regulation of the Pit-2 phosphate transporter retrovirus receptor by protein kinase C epsilon

The membrane receptors for the gibbon ape leukemia retrovirus and the ampho tropic murine retrovirus serve normal cellular functions as sodium-dependen t phosphate transporters (Pit-1 and Pit-2, respectively). Our earlier studi es established that activation of protein kinase C (PKC) by treatment of ce lls with phorbol 12-myristate 13-acetate (PMA) enhanced sodium-dependent ph osphate (Na/P-i) uptake, Studies now have been carried out to determine whi ch type of Na/P-i transporter (Pit-1 or Pit-2) is regulated by PKC and whic h PKC isotypes are involved in the up-regulation of Na/P-i uptake by the Na /P-i transporter/viral receptor. It was found that the activation of short term (2-min) Na/P-i uptake by PMA is abolished when cells are infected with amphotropic murine retrovirus (binds Pit-2 receptor) but not with gibbon a pe leukemia retrovirus (binds Pit-1 receptor), indicating that Pit-2 is the form of Na/P-i, transporter/viral receptor regulated by PKC, The PKC-media ted activation of Pit-2 was blocked by pretreating cells with the pan-PKC i nhibitor bisindolylmaleimide but not with the conventional PKC isotype inhi bitor Go 6976, suggesting that a novel PKC isotype is required to regulate Pit-2. Overexpression of PKC epsilon, but not of PKC alpha, -delta, or -zet a was found to mimic the activation of Na/P-i uptake. To further establish that PKC epsilon is involved in the regulation of Pit-2, cells were treated with PKC epsilon-selective antisense oligonucleotides, Treatment with PKC epsilon antisense oligonucleotides decreased the PMA-induced activation of Na/P-i uptake. These results indicate that PMA-induced stimulation of Na/P- i uptake by Pit-2 is specifically mediated through activation of PKC epsilo n.