Oncogene-mediated nuclear accumulation of lactate promotes epigenetic alterations to induce cancer cell proliferation.

Homeobox gene families are associated with embryonic development and organogenesis. Pieces of evidence suggest that these Homeobox genes are also crucial in facilitating oncogenesis when mutated or overexpressed. Paired homeodomain transcription factor-2 (PITX2), one of the members of this family, is involved in oncogenic regulation apart from its different development regulatory functions. PITX2 has been earlier shown to induce ovarian cancer cell proliferation through the activation of different signaling cascades. Increased cancer cell proliferation requires a constant supply of nutrients for both adenosine triphosphate and biomass synthesis, which is facilitated by altered cancer cell metabolism that includes enhanced glucose uptake and increased glycolytic rate. This present study highlights the involvement of PITX2 in enhancing the cellular glycolysis pathway in ovarian cancer cells through protein kinase B-phosphorylation (phospho-AKT). PITX2 expression correlates positively with that of the glycolytic rate-determining enzyme, lactate dehydrogenase-A (LDHA), in both high-grade serous ovarian cancer tissues and common ovarian cancer cell lines. Interestingly, transient localization of enzymatically active LDHA in the nucleus was observed in PITX2-overexpressed ovarian cancer cells. This nuclear LDHA produces higher concentrations of the glycolytic end product, lactate, which accumulates in the nuclear compartment resulting in decreased histone deacetylase (HDAC1/2) expression and increased histone acetylation at H3/H4. However, the mechanistic details of lactate-HDAC interaction are still elusive in the earlier reports. Our in silico studies elaborated on the interaction dynamics of lactate in the HDAC catalytic core through ligand-binding studies and molecular dynamics simulation approaches. Blocking lactate production by silencing LDHA reduced cancer cell proliferation. Thus, PITX2-induced epigenetic changes can lead to high cellular proliferation and increase the size of tumors in syngeneic mice as well. Taken together, this is the first report of its kind to show that the developmental regulatory homeobox gene PITX2 could enhance oncogenesis through enhanced glycolysis of tumor cells followed by epigenetic modifications.

SIRT6 promotes mitochondrial fission and subsequent cellular invasion in ovarian cancer.

Ovarian cancer ranks fifth in terms of cancer mortality in women due to lack of early diagnosis and poor clinical management. Characteristics like high cellular proliferation, EMT and metabolic alterations contribute to oncogenicity. Cancer, being a "metabolic disorder," is governed by various key regulatory factors like metabolic enzymes, oncogenes, and tumor suppressors. Sirtuins (SIRT1-SIRT7) belong to the group of NAD+ deacetylase and ADP-ribosylation enzymes that function as NAD+ sensors and metabolic regulators. Among sirtuin orthologs, SIRT6 emerges as an important oncogenic player, although its possible mechanistic involvement in ovarian cancer advancement is still elusive. Our data indicated a higher expression of SIRT6 in ovarian cancer tissues compared with the non-malignant ovarian tissue. Further, we observed that overexpression of SIRT6 enhances glycolysis and oxidative phosphorylation in ovarian cancer cells. The energy derived from these processes facilitates migration and invasion through invadopodia formation by reorganization of actin fibers. Mechanistically, SIRT6 has been shown to promote ERK1/2-driven activatory phosphorylation of DRP1 at serine-616, which has an obligatory role in inducing mitochondrial fission. These fragmented mitochondria facilitate cell movement important for metastases. siRNA-mediated downregulation of SIRT6 was found to decrease cellular invasion through compromised mitochondrial fragmentation and subsequent reduction in stress fiber formation in ovarian cancer cells. Thus, the present report establishes the impact of SIRT6 in the regulation of morphological and functional aspects of mitochondria that modulates invasion in ovarian cancer cells.

Correction to: Autophagy inhibition with chloroquine reverts paclitaxel resistance and attenuates metastatic potential in human nonsmall lung adenocarcinoma A549 cells via ROS mediated modulation of ß-catenin pathway.

The original version of this article unfortunately contained an error in acknowledgment text. The authors would like to include a statement: "Moumita Dasgupta is supported by Junior Research Fellowship from University Grant Commission, India." in acknowledgment section.

Autophagy inhibition with chloroquine reverts paclitaxel resistance and attenuates metastatic potential in human nonsmall lung adenocarcinoma A549 cells via ROS mediated modulation of ß-catenin pathway.

Paclitaxel is one of the most commonly used drugs for the treatment of nonsmall cell lung cancer (NSCLC). However acquired resistance to paclitaxel, epithelial to mesenchymal transition and cancer stem cell formation are the major obstacles for successful chemotherapy with this drug. Some of the major reasons behind chemoresistance development include increased ability of the cancer cells to survive under stress conditions by autophagy, increased expression of drug efflux pumps, tubulin mutations etc. In this study we found that inhibition of autophagy with chloroquine prevented development of paclitaxel resistance in A549 cells with time and potentiated the effect of paclitaxel by increased accumulation of superoxide-producing damaged mitochondria, with elevated ROS generation, it also increased the apoptotic rate and sub G0/ G1 phase arrest with time in A549 cells treated with paclitaxel and attenuated the metastatic potential and cancer stem cell population of the paclitaxel-resistant cells by ROS mediated modulation of the Wnt/ß-catenin signaling pathway, thereby increasing paclitaxel sensitivity. ROS here played a crucial role in modulating Akt activity when autophagy process was hindered by chloroquine, excessive ROS accumulation in the cell inhibited Akt activity. In addition, chloroquine pre-treatment followed by taxol (10 nM) treatment did not show significant toxicity towards non-carcinomas WI38 cells (lung fibroblast cells). Thus autophagy inhibition by CQ pre-treatment can be used as a fruitful strategy to combat the phenomenon of paclitaxel resistance development as well as metastasis in lung cancer.