Ser-486/491 phosphorylation and inhibition of AMPKα activity is positively associated with Gleason score, metastasis, and castration-resistance in prostate cancer: A retrospective clinical study

Abstract

Background: We previously demonstrated that adenosine monophosphate-activated protein kinase (AMPKα) activity is significantly inhibited by Ser-486/491 phosphorylation in cell culture and in vivo models of metastatic and castration-resistant prostate cancer, and hypothesized these findings may translate to clinical specimens.

Methods: In this retrospective, single-institution pilot study, 45 metastatic prostate cancer cases were identified within the University Hospitals Cleveland Medical Center Pathology Archive with both metastasis and matched primary prostate tumor specimens in formalin-fixed, paraffin-embedded blocks, and complete electronic medical records. Thirty non-metastatic, hormone-dependent prostate cancer controls, who were progression-free as defined by undetectable prostate specific antigen for at least 79.6 months (range 79.6-136.0 months), and matched metastatic cases based on age, race, and year of diagnosis. All specimens were collected from 1991 to 2014; primary tumor specimens were obtained via diagnostic biopsy or prostatectomy, and metastasis specimens obtained via surgery or perimortem. 5-μ sequential slides were processed for phospho-Ser-486/491 AMPKα₁ /α₂ , phospho-Thr-172 AMPKα, AMPKα₁ /α₂ , phospho-Ser-792 Raptor, phospho-Ser-79 acetyl-CoA carboxylase, and phospho-Ser-872, 3-hydroxy-3-methylglutaryl-CoA reductase immunohistochemistry to determine expression, phosphorylation pattern, and activity of AMPKα.

Results: Increased inhibitory Ser-486/491 AMPKα₁ /α₂ phosphorylation, increased AMPKα protein expression, decreased AMPKα activity, and loss of nuclear AMPKα and p-AMPKα are associated with prostate cancer progression to metastasis. Increased p-Ser-486/491 AMPKα₁ /α₂ was also positively correlated with higher Gleason grade and progression to castration-resistance.

Conclusions: p-Ser-486/491 AMPKα₁ /α₂ is a novel marker of prostate cancer metastasis and castration-resistance. Ser-486/491 phosphokinases should be pursued as targets for metastatic and castration-resistant prostate cancer chemotherapy.

Keywords: pathology; AMP-activated protein kinase; castration-resistant prostate cancer; clinical specimens; metastasis; prostatic neoplasms.

Figure 1.. Ser-486/491 AMPKα phosphorylation, AMPKα protein expression, and inhibition of AMPKα activity associated with prostate cancer metastasis.

Immunohistochemical staining for p-Ser-486/491 AMPKα₁/α₂, p-Thr-172 AMPKα, AMPKα, p-Ser-79 ACC, p-Ser-872 HMG-CoAR, and p-Ser-792 Raptor in representative specimens of non-metastatic cohort primary prostate tumor and metastatic cohort primary prostate tumor and metastases. Decrease in Ser-79 ACC, Ser-872 HMG-CoAR, and Ser-792 Raptor phosphorylation demonstrates decreased AMPKα activity.

Figure 2.. Prostate cancer metastasis is associated with loss of nuclear AMPKα and p-AMPKα expression.

Immunohistochemical staining for p-Ser-486/491 AMPKα₁/α₂, p-Thr-172 AMPKα, and AMPKα in samples representative of non-metastatic cohort primary prostate tumor and metastatic cohort primary prostate tumor and metastasis specimens analyzed. AMPKα and p-AMPKα becomes cytoplasmic localized with progression to metastasis.