Biology subjects

Herrera-Montavez, C.

Publications and source records attributed to Herrera-Montavez, C..

4 recordsLinked to original sources

bioRxiv2025

Human MutLa activates methylpurine DNA glycosylase to induce alkylation damage cytotoxicity

Alkylation chemotherapy is commonly used against tumors such as glioblastoma, yet resistance often develops through downregulation of mismatch repair (MMR). Previous work has established that loss of MMR prevents the excision of the thymine-containing strand across O6meG-T mismatches. Thus, MMR dysfunction is advantageous because it prevents a vicious cycle of attempted repair that leads to cell death. Here, we provide an alternative explanation to this prevailing mechanism of alkylation chemoresistance by MMR loss. We find that the MMR protein MutL physically and functionally interacts with the base excision repair (BER) enzyme methylpurine DNA glycosylase (MPG), which processes common alkylation adducts, such as 7meG and 3meA. Biochemical reconstitution demonstrates that MutL activates MPG glycosylase activity at least partly by promoting MPG substrate binding. This glycosylase stimulation requires ATP hydrolysis as well as the MLH1-interacting region on MPG. Both MutL or its ability to interact with MPG promote the generation of alkylation-induced abasic sites in cells, which contribute to the cytotoxicity of methyl methanesulfonate (MMS), an SN2 alkylating agent which does not produce O6meG. Our results provide new insight into the mechanism of alkylation chemoresistance and uncover an unappreciated crosstalk between MMR and base excision repair.

biochemistry↗

bioRxiv2025

Characterization of MEK1/2 Degraders Uncovers a Kinase-Independent Role for MEK1/2 in the Stabilization and Maturation of CRAF

Altered MAPK signaling frequently occurs in human disease. MEK1 and MEK2 (MEK1/2) are central protein kinases in the MAPK signaling cascade that phosphorylate ERK1/2 promoting cell growth. MEK1/2 degraders offer a strategy to characterize both kinase-dependent and independent functions of MEK1/2. Here, we discovered that MEK1/2 degradation, but not kinase inhibition, caused the subsequent degradation of upstream kinase CRAF via a cell-intrinsic mechanism. MEK1/2 binding to CRAF, but not MEK1/2 catalytic activity, was required for CRAF protein stability and maturation to a functional kinase. In the absence of MEK1/2, a minor pool of newly synthesized immature CRAF that had anti-apoptotic functions remained. Finally, we showed that a stable primed CRAF-MEK1/2 signaling complex existed in cells that required RAS binding to potentiate MEK-ERK phosphorylation. Together, weve discovered a previously unrecognized kinase-independent function of MEK1/2, while contextualizing MEK1/2 as an integral component of the CRAF activation cycle beyond the conventional CRAF-MEK kinase- substrate paradigm.

cancer biology↗

bioRxiv2023

MEK1/2-Targeting PROTACs Promote the Collateral Degradation of CRAF in KRAS Mutant Cells

Withdrawal StatementFollowing extensive additional studies, we discovered new findings that suggest that the degradation of CRAF by MS934 is not via collateral degradation through proximity to MEK1/2 but rather via a cell intrinsic mechanism that occurs post MEK1/2 degradation in KRAS mutant cells. We have performed extensive time course experiments exploring MS934-mediated degradation of CRAF, as well as additional MEK1/2 knockdown studies in several cell line models. Data from these studies showed that MEK1/2 proteins are degraded by MS934 several hours before CRAF protein and that genetic depletion of both MEK1 and MEK2 reduces CRAF protein levels equivalent to that observed with MS934. Together, these new findings suggest that CRAF degradation is not due to collateral proximity degradation by MS934 but rather due to a cell intrinsic mechanism post MEK1/2 protein depletion.

cancer biology↗

bioRxiv2021

MDR1 Drug Efflux Pump Promotes Intrinsic and Acquired Resistance to PROTACs in Cancer Cells

PROTACs (Proteolysis-Targeting Chimeras) represent a promising new class of drugs that selectively degrade proteins of interest from cells. PROTACs targeting oncogenes are avidly being explored for cancer therapies, with several currently in clinical trials. Drug resistance represents a significant challenge in cancer therapies, and the mechanism by which cancer cells acquire resistance to PROTACs remains poorly understood. Using proteomics, we discovered acquired and intrinsic resistance to PROTACs in cancer cells can be mediated by upregulation of the drug efflux pump MDR1. PROTAC-resistant cells could be re-sensitized to PROTACs through co-administering MDR1 inhibitors. Notably, co-treatment of MDR1-overexpressing colorectal cancer cells with MEK1/2 or KRASG12C degraders and the dual ErbB receptor/MDR1 inhibitor lapatinib exhibited potent drug synergy due to simultaneous blockade of MDR1 and ErbB receptor activity. Together, our findings suggest that concurrent blockade of MDR1 will likely be required in combination with PROTACs to achieve durable protein degradation and therapeutic response in cancer.

cancer biology↗