The folate-coupled enzyme MTHFD2 is a nuclear protein and promotes cell proliferation.

Folate metabolism is central to cell proliferation and a target of commonly used cancer chemotherapeutics. In particular, the mitochondrial folate-coupled metabolism is thought to be important for proliferating cancer cells. The enzyme MTHFD2 in this pathway is highly expressed in human tumors and broadly required for survival of cancer cells. Although the enzymatic activity of the MTHFD2 protein is well understood, little is known about its larger role in cancer cell biology. We here report that MTHFD2 is co-expressed with two distinct gene sets, representing amino acid metabolism and cell proliferation, respectively. Consistent with a role for MTHFD2 in cell proliferation, MTHFD2 expression was repressed in cells rendered quiescent by deprivation of growth signals (serum) and rapidly re-induced by serum stimulation. Overexpression of MTHFD2 alone was sufficient to promote cell proliferation independent of its dehydrogenase activity, even during growth restriction. In addition to its known mitochondrial localization, we found MTHFD2 to have a nuclear localization and co-localize with DNA replication sites. These findings suggest a previously unknown role for MTHFD2 in cancer cell proliferation, adding to its known function in mitochondrial folate metabolism.

Estrogen receptor-α, RBCK1, and protein kinase C ß 1 cooperate to regulate estrogen receptor-α gene expression.

Estrogen receptor α (ERα) is initially overexpressed in two-thirds of all breast cancers and is involved in its development and proliferation. We previously reported that the RanBP-type and C3HC4-type zinc finger containing 1 (RBCK1) interacts with the ERα promoter and that RBCK1 expression positively correlates with ERα levels, expression of ERα downstream target genes, and proliferation of breast cancer cells. Based on this, and that RBCK1 positively correlates with ERα expression in breast cancer samples, we propose RBCK1 as a potential therapeutic target in breast cancer acting as a modulator of ERα expression. To further explore this, the molecular mechanism by which RBCK1 regulates ERα expression has to be defined. Here, we show that ERα, RBCK1, and the RBCK1-interacting protein protein kinase C ß 1 (PKCß(I)) co-occupy a previously identified ERα binding region in the proximal ERα promoter. We describe a number of mechanistic details of this complex including that RBCK1 recruitment to the ERα promoter B is facilitated by ERα, which in turn facilitates PKCß(I) recruitment and PKCß(I)-dependent histone modifications. Furthermore, ERα regulation of its own mRNA expression is facilitated by RBCK1 recruitment, suggesting an ERα coactivator function of RBCK1. The interaction between RBCK1 and ERα was dependent on the E3 ubiquitin ligase domain of RBCK1 and the activating function-1 domain of ERα. The ligand-binding function of ERα does not influence the interaction with RBCK1. In summary, our data provide insight into the molecular mechanism by which ERα expression is modulated in breast cancer cells.