title: Calmodulin protects androgen receptor from calpain-mediated breakdown in prostate cancer cells.
abstract: Although inactivation of the androgen receptor (AR) by androgen-ablation or anti-androgen treatment has been frontline therapy for disseminated prostate cancer for over 60 years, it is not curative because castration-resistant prostate cancer cells retain AR activity. Therefore, curative strategy should include targeted elimination of AR protein. Since AR binds to calmodulin (CaM), and since CaM-binding proteins are targets of calpain (Cpn)-mediated proteolysis, we studied the role of CaM and Cpn in AR breakdown in prostate cancer cells. Whereas the treatment of prostate cancer cells individually with anti-CaM drug or calcimycin, which increases intracellular Ca(++) and activates Cpn, led to minimal AR breakdown, combined treatment led to a precipitous decrease in AR protein levels. This decrease in AR protein occurred without noticeable changes in AR mRNA levels, suggesting an increase in AR protein turnover rather than inhibition of AR mRNA expression. Thus, CaM inactivation seems to sensitize AR to Cpn-mediated breakdown in prostate cancer cells. Consistent with this possibility, purified recombinant human AR (rhAR) underwent proteolysis in the presence of purified Cpn, and the addition of purified CaM to the incubation blocked rhAR proteolysis. Together, these observations demonstrate that AR is a Cpn target and AR-bound CaM plays an important role in protecting AR from Cpn-mediated breakdown in prostate cancer cells. These observations raise an intriguing possibility that anti-CaM drugs in combination with Cpn-activating agents may offer a curative strategy for the treatment of prostate cancer, which relies on AR for growth and survival.
authors.affiliation: Vattikuti Urology Institute, Henry Ford Hospital, Detroit, Michigan 48202, USA.
authors.forename: Arun
authors.initials: A
authors.lastname: Sivanandam
authors.forename: Shalini
authors.initials: S
authors.lastname: Murthy
authors.forename: Kannagi
authors.initials: K
authors.lastname: Chinnakannu
authors.forename: V Uma
authors.initials: VU
authors.lastname: Bai
authors.forename: Sahn-Ho
authors.initials: SH
authors.lastname: Kim
authors.forename: Evelyn R
authors.initials: ER
authors.lastname: Barrack
authors.forename: Mani
authors.initials: M
authors.lastname: Menon
authors.forename: G Prem-Veer
authors.initials: GP
authors.lastname: Reddy
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: C410798:AR protein, human; D000970:Antineoplastic Agents; D002147:Calmodulin; D007476:Ionophores; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D011944:Receptors, Androgen; D011994:Recombinant Proteins; D013449:Sulfonamides; D014268:Trifluoperazine; D000001:Calcimycin; C017967:W 7; C034700:N-(6-aminohexyl)-1-naphthalenesulfonamide; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002154:Calpain; D002118:Calcium