Mir143 expression inversely correlates with nuclear ERK5 immunoreactivity in clinical prostate cancer

Abstract

Background: Aberrant mitogen/extracellular signal-regulated kinase 5 (MEK5)-extracellular signal-regulated protein kinase 5 (ERK5)-mediated signalling has been implicated in a number of tumour types including prostate cancer (CaP). The mechanism for ERK5 activation in CaP remains to be fully elucidated. Studies have recently implicated the role of microRNA (miRNA) mir143 expression in the regulation of ERK5 expression.

Methods: We utilised a tissue microarray (TMA) of 530 CaP cores from 168 individual patients and stained for both mir143 and ERK5. These TMAs were scored by a combination of observer and automated methods.

Results: We observed a strong inverse relation between ERK5 and mir143, which manifested itself most strongly in the subgroup of 417 cores with non-zero mir143 and ERK5 immunoreactivity, or with only one of mir143 or ERK5 being zero (cc=0.2558 and P<0.0001). Mir143 neither correlate with Gleason scores or prostate-specific antigen levels, nor was it a predictor of disease-specific survival on univariate analysis.

Conclusion: Although the mechanism for ERK5 activation in CaP remains to be fully elucidated, we have further validated the potential role of mir143 in regulating ERK5 levels in the clinical context. In addition, we demonstrate that the automated counting method for nuclear ERK5 is a clinically useful alterative to observer counting method in patient stratification in the context of ERK5 targeting therapy.

Figure 1

Bar charts summarising the distribution (in percentage) among the CaP cases with different expression scores (0–3) for mir143 (A) and ERK5 (B). (C) The correlative analysis for mir143 and ERK5 expression (Spearman’s ρ=0.098, P=0.0238). Yellow box highlights samples with scores for mir143>0, whereas red box highlights samples with scores for ERK>0. The inverse relationship between the two markers manifests itself most strongly in the subgroup of 417 cores with non-zero mir143 and ERK5 readings (yellow and red boxes combined), or with only one of mir143 or ERK5 being zero (yellow and red boxes, respectively). Representative images showing an inverse relationship between mir143 and ERK5 expression. D/E (Gleason 5) and F/G (Gleason 3) are paired images from two individual patients. For each patient’s samples, namely D/E and F/G, represent tissue from sequential sections were analysed. D shows suppressed mir143 expression, whereas F demonstrated detectable mir143 transcript expression (red arrows). E and G demonstrate upregulated and negligible nuclear ERK5 immunoreactivity, respectively. Black bar measures 200 mm ( × 20 objective).

Figure 2

Gleason pattern grade 3 (A–C) and Gleason pattern grade 5 (D–F) tumours were scored using the automated system. A and D demonstrate low and high ERK5 immunoreactivity in Gleason grade 3 and 5 tumours, respectively. B and E show all of the epithelial nuclei highlighted green, whereas C and F show the classification of ERK5 within each core as positive (red) or negative (blue) based on the adjustable input parameters (see details in Materials and Method section). Scores for sections represented in A–C were negative (0), weak (1), moderate (2) and strong (3) for nuclear immunoreactivity at 88%, 0%, 11%, 1%, respectively, giving a histoscore of 25. Score for sections in D–F were negative, weak, moderate and strong nuclei at 17%, 0%, 31%, 52%, respectively, giving a histoscore of 218. G–I represent typical in situ hybridisation images for mir143 expression: high, moderate to low for G, H and I, respectively. Black bar measures 200 mm ( × 20 objective).