title: Phosphorylation of Par-4 by protein kinase A is critical for apoptosis.
abstract: Despite distinct dissimilarities, diverse cancers express several common protumorigenic traits. We present here evidence that the proapoptotic protein Par-4 utilizes one such common tumorigenic trait to become selectively activated and induce apoptosis in cancer cells. Elevated protein kinase A (PKA) activity noted in cancer cells activated the apoptotic function of ectopic Par-4 or its SAC (selective for apoptosis induction in cancer cells) domain, which induces apoptosis selectively in cancer cells and not in normal or immortalized cells. PKA preferentially phosphorylated Par-4 at the T155 residue within the SAC domain in cancer cells. Moreover, pharmacological-, peptide-, or small interfering RNA-mediated inhibition of PKA activity in cancer cells resulted in abrogation of both T155 phosphorylation and apoptosis by Par-4. The mechanism of activation of endogenous Par-4 was similar to that of ectopic Par-4, and in response to exogenous stimuli, endogenous Par-4 induced apoptosis by a PKA- and phosphorylated T155-dependent mechanism. Enforced elevation of PKA activity in normal cells resulted in apoptosis by the SAC domain of Par-4 in a T155-dependent manner. Together, these observations suggest that selective apoptosis of cancer cells by the SAC domain of Par-4 involves phosphorylation of T155 by PKA. These findings uncover a novel mechanism engaging PKA, a procancerous activity commonly elevated in most tumor cells, to activate the cancer selective apoptotic action of Par-4.
authors.affiliation: Department of Radiation Medicine, University of Kentucky, Combs Research Building, Rm. 303, 800 Rose Street, Lexington, KY 40536, USA.
authors.forename: Sushma
authors.initials: S
authors.lastname: Gurumurthy
authors.forename: Anindya
authors.initials: A
authors.lastname: Goswami
authors.forename: Krishna Murthi
authors.initials: KM
authors.lastname: Vasudevan
authors.forename: Vivek M
authors.initials: VM
authors.lastname: Rangnekar
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008297:Male; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D051017:Apoptosis Regulatory Proteins; D047908:Intracellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; C101296:prostate apoptosis response-4 protein; D049452:Green Fluorescent Proteins; D017868:Cyclic AMP-Dependent Protein Kinases