Natural compounds solasonine and alisol B23-acetate target GLI3 signaling to block oncogenesis in MED12-altered breast cancer.

Breast cancer remains to be the second leading cause of cancer deaths worldwide thereby highlighting the critical need to find superior treatment strategies for this disease. In the current era of cancer treatment, personalized medicine is garnering much attention as this type of treatment is more selective thereby minimizing harmful side effects. Personalized medicine is dependent upon knowing the underlying genetic landscape of the initial tumor. In our study, we focused our efforts on a specific subset of breast cancer that harbors genetic alterations in the Mediator subunit 12 (MED12). Our results show that loss of MED12 leads to enhanced cellular proliferation and colony formation of breast cancer cells through a mechanism that involves activation of GLI3-dependent SHH signaling, a pathway that is central to breast development and homeostasis. To find a personalized treatment option for this subset of breast cancer, we employed a natural compound screening strategy which uncovered a total of ten compounds that selectively target MED12 knockdown breast cancer cells. Our results show that two of these ten compounds, solasonine and alisol B23-acetate, block GLI3-dependent SHH signaling which leads to a reversal of enhanced cellular proliferation and colony formation ability. Thus, our findings provide promising insight into a novel personalized treatment strategy for patients suffering from MED12-altered breast cancer.

Biochemical and biophysical characterization of the nucleic acid binding properties of the RNA/DNA binding protein EWS.

EWS is a member of the FET family of RNA/DNA binding proteins that regulate crucial phases of nucleic acid metabolism. EWS comprises an N-terminal low-complexity domain (LCD) and a C-terminal RNA-binding domain (RBD). The RBD is further divided into three RG-rich regions, which flank an RNA-recognition motif (RRM) and a zinc finger (ZnF) domain. Recently, EWS was shown to regulate R-loops in Ewing sarcoma, a pediatric bone and soft-tissue cancer in which a chromosomal translocation fuses the N-terminal LCD of EWS to the C-terminal DNA binding domain of the transcription factor FLI1. Though EWS was shown to directly bind R-loops, the binding mechanism was not elucidated. In the current study, the RBD of EWS was divided into several constructs, which were subsequently assayed for binding to various nucleic acid structures expected to form at R-loops, including RNA stem-loops, DNA G-quadruplexes, and RNA:DNA hybrids. EWS interacted with all three nucleic acid structures with varying affinities and multiple domains contributed to binding each substrate. The RRM and RG2 region appear to bind nucleic acids promiscuously while the ZnF displayed more selectivity for single-stranded structures. With these results, the structural underpinnings of EWS recognition and binding of R-loops and other nucleic acid structures is better understood.

The role of mediator subunit 12 in tumorigenesis and cancer therapeutics.

Mediator complex subunit 12 (MED12) is a subunit of Mediator, a large multi-subunit protein complex that acts an important regulator of transcription. Specifically, MED12 is an integral part of the kinase module of Mediator along with MED13, CyclinC (CycC) and CDK8. Structural studies have indicated that MED12 makes a direct connection to CycC through a specific interface and thereby functions to create a link between MED13 and CycC-CDK8. Disruption of the MED12-CycC interface often leads to dysregulated CDK8 kinase activity, which has important physiological implications. For example, a number of studies have indicated that mutations within MED12 can lead to the formation of benign or malignant tumors, either as a result of MED12-CycC disruption or through distinct independent mechanisms. Furthermore, recent studies have indicated that the N-terminal portion of MED12 forms a direct connection to CDK8. Mutations within MED12 do not appear to disrupt the physical connection to CDK8, but rather abrogate CDK8 kinase activity. Thus, mutations in MED12 can cause disruption of CDK8 kinase activity through two separate mechanisms. The aim of the present review article was to discuss the MED12 mutational landscape in a variety of benign and malignant tumors, as well as the mechanistic basis behind tumorigenesis. Furthermore, the link between MED12 and drug resistance has also been discussed, as well as potential cancer therapeutics related to MED12-altered tumors.