PP1, PKA and DARPP-32 in breast cancer: A retrospective assessment of protein and mRNA expression

Abstract

Cyclic AMP-dependent protein kinase A (PKA) and protein phosphatase 1 (PP1) are proteins involved in numerous essential signalling pathways that modulate physiological and pathological functions. Both PP1 and PKA can be inhibited by dopamine- and cAMP-regulated phosphoprotein 32 kD (DARPP-32). Using immunohistochemistry, PKA and PP1 expression was determined in a large primary breast tumour cohort to evaluate associations between clinical outcome and clinicopathological criteria (n > 1100). In addition, mRNA expression of PKA and PP1 subunits was assessed in the METABRIC data set (n = 1980). Low protein expression of PKA was significantly associated with adverse survival of breast cancer patients; interestingly, this relationship was stronger in ER-positive breast cancer patients. PP1 protein expression was not associated with patient survival. PKA and PP1 subunit mRNA was also assessed; PPP1CA, PRKACG and PRKAR1B were associated with breast cancer-specific survival. In patients with high expression of DARPP-32, low expression of PP1 was associated with adverse survival when compared to high expression in the same group. PKA expression and PP1 expression are of significant interest in cancer as they are involved in a wide array of cellular processes, and these data indicate PKA and PP1 may play an important role in patient outcome.

Keywords: DARPP-32; PKA; PP-1.

FIGURE 1

Heat map of DARPP‐32, PP1, PKA and Cdk5 expression (A). Representative photomicrographs of high (B) and low (C) PKA expression, and high (D) and low (E) PP1 expression are shown at 10× magnification with a 20× magnification inset box. Scale bar represents 100 µM. Similarity matrix of Pearson's correlation coefficients between protein expression (F)

FIGURE 2

Kaplan‐Meier analysis of PKA (A) and PKA expression in oestrogen receptor–positive breast cancer (B) and cytoplasmic (C) and nuclear (D) PP1 expression where the impact of low (grey line) and high (black line) expression is shown

FIGURE 3

Kaplan‐Meier analysis of combined protein expression. A, PKA and cytoplasmic DARPP‐32 expression; high PKA and high DARPP‐32 (orange), high PKA and low DARPP‐32 (green), low PKA and high DARPP‐32 (pink) and low PKA and low DARPP‐32 (blue) are shown. B, PKA and cytoplasmic Cdk5 expression; high PKA and high Cdk5 (orange), high PKA and low Cdk5 (pink), low PKA and high Cdk5 (green) and low PKA and low Cdk5 (blue) are shown. C, PP1 and cytoplasmic DARPP‐32 expression; high PP1 and high DARPP‐32 (orange), high PP1 and low DARPP‐32 (green), low PP1 and high DARPP‐32 (pink) and low PP1 and low DARPP‐32 (blue) are shown. D, PP1 and Cdk5 expression; high PP1 and high Cdk5 (orange), high PP1 and low Cdk5 (pink), low PP1 and high Cdk5 (green) and low PP1 and low Cdk5 (blue) are shown

FIGURE 4

Heat map of PRKACA, PRKACB, PRKACG, PRKAR1A, PRKAR1B, PRAKAR2A, PRKAR2B, PPP1CA, PPP1CB, PPP1CC, PPP1R1B and CDK5 expression (A), and Pearson's correlation coefficients between them (B)