SOX2 and PRAME in the "reprogramming" of seminoma cells.

BACKGROUND

In recent years, several studies investigated the complex process called "reprogramming" of seminoma (S) cells. The accepted pathogenetic model is a complex network including SOX2, SOX17, OCT3/4 and PRAME, which modulates the epigenetic transcription of numerous downstream genes and drives a divergent gene expression profile resulting in the transition from pure S (P-S) to S component (S-C) of mixed germ cell tumors of the testis (M-GCTT), and finally to embryonal carcinoma (EC). Herein, we tested a large cohort of GCTT with SOX2 and PRAME to evaluate their expression in the evolutionary steps of GCTT and verify if the modulation in the expression of these two molecules could be relevant for the fate of GCTT.

METHODS

We tested 43, 19 and 17 consecutive and retrospectively enrolled cases of GCTT, germ cell neoplasia in situ (GCNIS) and uninvolved background testes (UBT), respectively. SOX2 and PRAME expressions have been evaluated with H-score and compared by adopting the appropriate statistic tests (Student's t-test and Mann-Whitney U test).

RESULTS

We found that SOX2 was more expressed by nonseminomatous-GCTT (NS-GCTT) (p < 0.001) and EC (p < 0.001) rather than S; by contrast, PRAME showed an opposite expression profile being expressed by S but not by NS-GCTT (p < 0.001) and EC (p < 0.001). S-C showed different expressions of SOX2 and PRAME compared to both P-S (p = 0.002 and <0.001, respectively) and EC (p < 0.001 and 0.042, respectively), with intermediate values between these latter two categories. GCNIS and UBT showed no expression of SOX2 (scattered positive Leydig cells) but high H-score levels of PRAME.

CONCLUSIONS

SOX2 and PRAME are differentially expressed and specularly modulated during the "reprogramming" of S cells [P-S (high levels of PRAME, no expression/low levels of SOX2) → S-C (intermediate levels of PRAME, intermediate levels of SOX2) → EC (no expression/low levels of PRAME, high levels of SOX2)], therefore supporting a complex pathogenetic model where the interactions between these two molecules are crucial in determining the fate of GCTT.