title: HIV-1 Tat-peptide inhibits protein kinase C and protein kinase A through substrate competition.
abstract: HIV-1 Tat-peptide is widely used as a vector for cargo delivery into intact cells. As a cationic, arginine-rich peptide it can readily penetrate the plasma membrane and facilitate the penetration of impermeable bioactive molecules such as proteins, peptides, nucleic acids and drugs. Although at first considered as an inert vector, recent studies have however shown that it might have effects on its own on various cellular processes. In the present study we have investigated the effects of the Tat-peptide(48-60) on two basic serine/threonine kinases, protein kinase C and A, since earlier studies have shown that certain arginine-rich peptides or proteins might have a modulatory effect on their activity. In in vitro studies, Tat-peptide inhibited PKC alpha in a concentration-dependent manner with an IC(50)-value of 22nM and PKA with an IC(50)-value of 1.2 microM. The mode of inhibition was studied in the presence of increasing concentrations of a substrate peptide or ATP. Tat-peptide competed with the kinase substrates, however it did not compete with ATP. In a panel of 70 kinases Tat-peptide showed inhibitory activity at least towards other AGC-family kinases (PKB, SGK1, S6K1, MSK1), CAMK-family kinases (CAMK1 and MELK) and a STE family kinase (MKK1). In HeLa cells Tat-peptide inhibited the phorbol ester-evoked ERK1/2 phosphorylation suggesting that Tat inhibited PKC also in intact cells. In thyroid cells Tat-peptide attenuated sphingosylphosphorylcholine-evoked Ca(2+)-fluxes, which have earlier been shown to be dependent on PKC. Taken together, these results indicate that the Tat-peptide(48-60) is a potent inhibitor which binds to the substrate binding site of the basophilic kinase domain.
authors.affiliation: University of Helsinki, Finland. elina.ekokoski@helsinki.fi
authors.forename: Elina
authors.initials: E
authors.lastname: Ekokoski
authors.forename: Olli
authors.initials: O
authors.lastname: Aitio
authors.forename: Kid
authors.initials: K
authors.lastname: Törnquist
authors.forename: Jari
authors.initials: J
authors.lastname: Yli-Kauhaluoma
authors.forename: Raimo K
authors.initials: RK
authors.lastname: Tuominen
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology*; D010455:Peptides / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013961:Thyroid Gland / Q000378:metabolism; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D010446:Peptide Fragments; D010455:Peptides; D054322:tat Gene Products, Human Immunodeficiency Virus; C422951:tat peptide (48-60), Human immunodeficiency virus 1; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D002118:Calcium