Pancreatic ductal adenocarcinoma (PDAC) harbors complex molecular alterations and remains a lethal disease. Aberrant TGF-β/Smads signaling is a well-known mechanism involved in the progression of PDACs. However, loss of Smad4 expression is reported in only ~50% of PDACs and is generally associated with worse prognosis. Investigating additional prognostic markers is warranted. PPM1A is a phosphatase that dephosphorylates TGF-β-activated Smad2/3 and inactivates the TGF-β signaling. Little is known about the clinical significance of PPM1A in PDACs and its functional relationship to Smad4. In this study, PPM1A and Smad4 immunohistochemistry was assessed in 180 R0 resected human PDACs. PPM1A was lost in 41.7% cases, whereas Smad4 was lost in 45.7% cases. The median survival rate with negative and positive PPM1A was 10.9 and 16.8 months, respectively. Loss of PPM1A was significantly associated with larger tumor size and higher stage and was an independent predictor of unfavorable outcomes. Intriguingly, the overall survival of this cohort was divided into 3 groups based on the expression pattern of PPM1A and Smad4, with the Smad4+/PPM1A+ pattern associated with favorable survival, the Smad4+/PPM1A- or Smad4-/PPM1A- pattern associated with unfavorable, and the PPM1A+/Smad4- pattern fell between these 2 groups. In 82 cases with negative Smad4, PPM1A or P-Smad2/3 expression was retained. Using a SMAD4-deficient human PDAC cell line, BxPC3, we further demonstrated that TGF-β1 treatment induced PPM1A and P-Smad2/3 expression in this cell line. PPM1A and Smad4 immunohistochemistry in surgical specimens may provide more accurate prognostic stratification for patients with PDAC.
Keywords: Immunohistochemistry; PPM1A; Pancreatic ductal adenocarcinoma; Phosphatase; Prognosis, marker; Smad4; TGF-β.
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