Implications of MTHFD2 expression in renal cell carcinoma aggressiveness

Abstract

Renal cell carcinoma (RCC) is the most common type of cancer in kidney and is often diagnosed in advanced stages. Until now, there is no reliable biomarker to assess tumor prognosis during histopathological diagnosis. The Methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) overexpression has been suggested as prognostic indicator for RCC, however, its protein profile needs to be clarified. This study investigated the MTHFD2 expression in different RCC cohorts, associating it with tumor characteristics and prognostic factors. Gene expression comparisons between non-neoplastic (NN) and tumor samples, as well as patients' survival analysis, were assessed using KM-Plotter tool. MTHFD2 protein pattern was evaluated in 117 RCC by immunohistochemistry and associations with prognosis, clinical and pathological data were investigated. The tumors exhibited higher MTHFD2 transcript levels than NN, being even higher in the metastatic group. Opposite gene expression patterns were found among clear cell renal cell carcinoma (ccRCC) and pappilary renal cell carcinoma (pRCC) subtypes, showing higher and lower expressions compared to NN samples respectively. Overexpression was associated with shorter overall survival for ccRCC and pRCC subtypes, and shorter recurrence-free survival for pRCC. The immunolabeling profile varied according to tumor subtypes, with lower intensity and expression scores in ccRCC compared to pRCC and to chromophobe renal cell carcinoma (chRCC). MTHFD2 protein expression was associated with larger tumors and higher Fuhrman grades. Although prognostic value of protein immunostaining was not confirmed, patients with higher MTHFD2 tended to have lower survival rates in the pRCC group. The results highlight MTHFD2 different patterns according to RCC histological subtypes, revealing marked variations at both the genetic and protein levels. The mRNA indicated tumor prognosis, and greater expression in the tumor samples. Although MTHFD2 immunolabeling suggests tumor aggressiveness, it needs to be validated in other cohorts as potential prognostic factor.

Fig 1. MTHFD2 gene expression in renal cell carcinoma.

(A) Comparison between tumor and non-neoplastic samples analyzed from the Gene chip database. (B-D) Expression in ccRCC, pRCC and chRCC histological subtypes compared to non-neoplastic specimens investigated in the Pan-cancer database.

Fig 2. Associations of MTHFD2 gene pattern with patients’ survival.

(A) and (C) Overall survivals in the ccRCC and pRCC cohorts. (B) and (D) Recurrence-free survivals in patients with ccRCC and pRCC. Kaplan-Meier curves and log-rank test. Pan-cancer database.

Fig 3. MTHFD2 protein expression in renal cell carcinoma by immunohistochemistry.

(A) Representative image of ccRCC case with weak intensity. (B) Representative image of pRCC case with strong intensity. (C) chRCC case with moderate intensity. (D) Intensity immunolabeling variation between RCC subtypes. (E) Comparison of expression scores between RCC subtypes. Kruskal-Wallis test.

Fig 4. MTHFD2 protein expression scores according to renal cell carcinoma Fuhrman grades.

(A) Increased immunolabeling score in tumors with Fuhrman grades 3 and 4, considering all histological subtypes. (B) Significant differences between grades 1 and 3, considering all histological subtypes. (C) Scores according to Fuhrman grades 1 and 2 versus 3 and 4 in the clear cell subtype. (D) Scores according to Fuhrman grades separately.