Activated MKK3/MYC crosstalk impairs dabrafenib response in BRAFV600E colorectal cancer leading to resistance.

Colorectal cancer (CRC) patients with BRAF mutations develop resistance to BRAF inhibitors at a very early stage. Understanding the molecular mechanisms involved in BRAF inhibitor resistance is critical for the development of novel therapeutic opportunities for this subtype of CRC patients. CRC cells bearing BRAF mutations are mostly sensitive to the abrogation of Mitogen-Activated Protein Kinase Kinase 3 (MKK3), a specific activator of p38MAPKs signaling, suggesting that BRAF alterations might addict CRC cells to the MKK3/p38MAPK signaling. Interestingly, publicly available gene expression profiling data show significantly higher MKK3 transcript levels in CRC lines with acquired resistance to BRAF inhibitors. Herein, we investigated the roles of MKK3 in the response to BRAF targeting (dabrafenib) with COLO205 and HT29 BRAFV600E CRC lines and derived dabrafenib-resistant (DABR) sublines. Dabrafenib treatments reduce MKK3 activation by inducing autophagy in parental but not DABR cells. The MKK3 knockdown induces cell death in DABR cells, whereas ectopic MKK3 expression reduces dabrafenib sensitivity in parental cells. Mechanistically, activated MKK3 interacts and co-localizes with c-Myc oncoprotein (MYC), sustaining MYC protein stability and thus preventing the dabrafenib induced effects in CRC DABR cells both in vitro and in vivo. Overall, we identify a novel molecular mechanism beyond the dabrafenib resistance, shedding light on an uncovered vulnerability for the development of novel therapeutic opportunities in BRAFV600E CRC.

Dissection of the MKK3 Functions in Human Cancer: A Double-Edged Sword?

The role played by MKK3 in human cancer is controversial. MKK3 is an evolutionarily conserved protein kinase that activates in response to a variety of stimuli. Phosphorylates, specifically the p38MAPK family proteins, contribute to the regulation of a plethora of cellular processes such as proliferation, differentiation, apoptosis, invasion, and cell migration. Genes in carcinogenesis are classified as oncogenes and tumor suppressors; however, a clear distinction is not always easily made as it depends on the cell context and tissue specificity. The aim of this study is the examination of the potential contribution of MKK3 in cancer through a systematic analysis of the recent literature. The overall results reveal a complex scenario of MKK3's involvement in cancer. The oncogenic functions of MKK3 were univocally documented in several solid tumors, such as colorectal, prostate cancer, and melanoma, while its tumor-suppressing functions were described in glioblastoma and gastric cancer. Furthermore, a dual role of MKK3 as an oncogene as well as tumor a suppressor has been described in breast, cervical, ovarian, liver, esophageal, and lung cancer. However, overall, more evidence points to its role as an oncogene in these diseases. This review indicates that the oncogenic and tumor-suppressing roles of MKK3 are strictly dependent on the tumor type and further suggests that MKK3 could represent an efficient putative molecular target that requires contextualization within a specific tumor type in order to adequately evaluate its potential effectiveness in designing novel anticancer therapies.

The p38 MAPK Signaling Activation in Colorectal Cancer upon Therapeutic Treatments.

Pharmacological treatment of colorectal carcinoma currently proceeds through the administration of a combination of different chemotherapeutic agents. In the case of rectal carcinoma, radiation therapy also represents a therapeutic strategy. In an attempt at translating much-needed new targeted therapy to the clinics, p38 mitogen activated protein kinase (MAPK) inhibitors have been tested in clinical trials involving colorectal carcinoma patients, especially in combination with chemotherapy; however, despite the high expectations raised by a clear involvement of the p38 MAPK pathway in the response to therapeutic treatments, poor results have been obtained so far. In this work, we review recent insights into the exact role of the p38 MAPK pathway in response to currently available therapies for colorectal carcinoma, depicting an intricate scenario in which the p38 MAPK node presents many opportunities, as well as many challenges, for its perspective exploitation for clinical purposes.

MKK3 sustains cell proliferation and survival through p38DELTA MAPK activation in colorectal cancer.

Colorectal cancer (CRC) is one of the most common malignant tumors worldwide and understanding its underlying molecular mechanisms is crucial for the development of therapeutic strategies. The mitogen-activated protein kinase-kinase 3 (MKK3) is a specific activator of p38 MAP kinases (p38 MAPKs), which contributes to the regulation of several cellular functions, such as proliferation, differentiation, apoptosis as well as response to drugs. At present, the exact MKK3/p38 MAPK pathway contribution in cancer is heavily debated because of its pleiotropic function. In this work, we retrospectively explored the prognostic and pathobiologic relevance of MKK3 in a cohort of CRC patients and assessed MKK3 molecular functions in a panel of CRC lines and colonocytes primary cultures. We found increased MKK3 levels in late-stage CRC patients which correlated with shorter overall survival. Herein, we report that the MKK3 targeting by inducible RNA interference univocally exerts antitumor effects in CRC lines but not in primary colonocytes. While MKK3 depletion per se affects growth and survival by induction of sustained autophagy and death in some CRC lines, it potentiates response to chemotherapeutic drug 5-fluorouracil (5-FU) in all of the tested CRC lines in vitro. Here, we demonstrate for the first time that in CRC the MKK3 specifically activates p38delta MAPK isoform to sustain prosurvival signaling and that such effect is exacerbated upon 5-FU challenge. Indeed, p38delta MAPK silencing recapitulates MKK3 depletion effects in CRC cells in vitro and in vivo. Overall, our data identified a molecular mechanism through which MKK3 supports proliferation and survival signaling in CRC, further supporting MKK3 as a novel and extremely attractive therapeutic target for the development of promising strategies for the management of CRC patients.

Insights of Crosstalk between p53 Protein and the MKK3/MKK6/p38 MAPK Signaling Pathway in Cancer.

TP53 is universally recognized as a pivotal protein in cell-cycle fate and apoptotic induction and, unsurprisingly, it is one of the most commonly hijacked control mechanisms in cancer. Recently, the kinase MKK3 emerged as a potential therapeutic target in different types of solid tumor being linked to mutant p53 gain-of-function. In this review, we summarize the delicate relationship among p53 mutational status, MKK3/MKK6 and the downstream activated master kinase p38MAPK, dissecting a finely-tuned crosstalk, in a potentially cell-context dependent scenario that urges towards a deeper characterization of the different molecular players involved in this signaling cascade and their interactions.