High DNA Methyltransferase 3B Expression Mediates 5-aza-deoxycytidine Hypersensitivity in Testicular Germ Cell Tumors

摘要

Testicular germ cell tumors (TGCTs) are the most common solid tumors of 15–35 year old men. TGCT patients are frequently cured with cytotoxic cisplatin-based therapy. However, TGCT patients refractory to cisplatin-based chemotherapy have a poor prognosis, as do those having a late relapse. Pluripotent embryonal carcinomas (ECs) are the malignant counterparts to embryonic stem (ES) cells and are considered the stem cells of TGCTs. Here we demonstrate that human EC cells are highly sensitive to 5-aza-deoxycytidine (5-aza-CdR) as compared to somatic solid tumor cells. Decreased proliferation and survival with low nanomolar concentrations of 5-aza-CdR is associated with ATM activation, H2AX phosphorylation, increased expression of p21, and the induction of genes known to be methylated in TGCTs (MGMT, RASSF1A and HOXA9). Notably, 5-aza-CdR hypersensitivity is associated with markedly abundant expression of the pluripotency-associated DNA methyltransferase 3B (DNMT3B) as compared to somatic tumor cells. Knockdown of DNMT3B in EC cells results in substantial resistance to 5-aza-CdR, strongly indicating that 5-aza-CdR sensitivity is mechanistically linked to high levels of DNMT3B. Intriguingly, cisplatin-resistant EC cells retain an exquisite sensitivity to low dose 5-aza-CdR treatment and pretreatment of 5-aza-CdR re-sensitizes these cells to cisplatin-mediated toxicity. This re-sensitization is also partially dependent on high DNMT3B levels. These novel findings indicate that high expression of DNMT3B, a likely byproduct of their pluripotency and germ cell origin, sensitizes TGCT-derived EC cells to low dose 5-aza-CdR treatment.