Biology subjects

Garcia-Gutierrez, L.

Publications and source records attributed to Garcia-Gutierrez, L..

4 recordsLinked to original sources

bioRxiv2022

MYC directly transactivates CR2/CD21, the receptor of the Epstein-Barr virus, and enhances the viral infection of Burkitt lymphoma cells

The molecular hallmark of Burkitt lymphoma (BL) is a chromosomal translocation that results in deregulated expression of MYC oncogene. This translocation is present in virtually all BL. MYC is an oncogenic transcription factor deregulated in about half of total human tumors, by translocation or other mechanisms. Transcriptomic studies reveal more than 1000 genes regulated by MYC but a much smaller fraction of these genes is directly activated by MYC. All the endemic BL and many sporadic BL cells are associated to the Epstein-Barr virus (EBV) infection. The currently accepted mechanism for the MYC and BL association is that EBV is the causing agent inducing MYC translocation. Complement receptor 2 or CR2 (also called CD21) is a membrane protein that serves as EBV receptor in lymphoid cells. Here we show that CR2 is a direct MYC target gene. This conclusion is based on several evidences. First, MYC downregulation is linked to CR2 downregulation both in proliferating and in arrested cells. Second, MYC binds human CR2 promoter and this binding depends on E-box elements. Third, MYC activates CR2 promoter in an E-box dependent manner. Four, MYC activates CR2 transcription in the absence of protein synthesis. Importantly, MYC also induces CR2 expression in mouse primary B cells. Thus, CR2 is a bona fide MYC direct target gene. Moreover, higher MYC expression levels in Burkitt lymphoma-derived cells result in a more efficient EBV infection. We propose an alternative mechanism compatible with the correlation between EBV infection and MYC translocation observed in endemic BL, i.e., that deregulated MYC in BL cells occurs first and favors the EBV infection.

cancer biology↗

bioRxiv2022

Proteasomal downregulation of the pro-apoptotic MST2 pathway contributes to BRAF inhibitor resistance in melanoma

The RAS-RAF-MEK-ERK pathway is hyperactivated in almost all malignant melanomas, and mutations in BRAF or NRAS account for most of these cases. BRAF inhibitors are highly efficient for treating patients with BRAFV600E mutations, but tumours frequently acquire resistance within a few months. Multiple resistance mechanisms have been identified, due to mutations or network adaptations that revive ERK signalling. We have previously shown that RAF proteins inhibit the MST2 proapoptotic pathway in a kinase independent fashion. Here, we have investigated the role of the MST2 pathway in mediating resistance to BRAF inhibitors. We show that the BRAFV600E mutant protein, but not the wildtype BRAF protein, strongly binds to MST2 and inhibits MST2 pro-apoptotic signalling. Downregulation of MST2 reduces BRAF inhibitor induced apoptosis. In BRAF inhibitor resistant cell lines MST2 pathway proteins are downregulated by ubiquitination and subsequent proteasomal degradation rendering cells refractory to MST2 pathway induced apoptosis. Restoration of apoptosis can be achieved by increasing MST2 pathway protein expression using proteasome inhibitors. In summary, we show that the MST2 pathway plays a role in the acquisition of BRAF inhibitor resistance in melanoma.

molecular biology↗

bioRxiv2019

BAX and SMAC Regulate Bistable Properties of the Apoptotic Caspase System

The initiation of apoptosis is a core mechanism in cellular biology by which organisms control the removal of damaged or unnecessary cells. The irreversible activation of caspases is essential for apoptosis, and mathematical models have demonstrated that the process is tightly regulated by positive feedback and a bistable switch. BAX and SMAC are often dysregulated in diseases such as cancer or neurodegeneration and are two key regulators that interact with the caspase system generating the apoptotic switch. Here we present a mathematical model of how BAX and SMAC control the apoptotic switch. Formulated as a system of ordinary differential equations, the model summarises experimental and computational evidence form the literature and incorporates the biochemical mechanisms of how BAX and SMAC interact with the components of the caspase system. Using simulations and bifurcation analysis, we find that both BAX and SMAC regulate the time-delay and activation threshold of the apoptotic switch. Interestingly, the model predicted that BAX (not SMAC) controls the amplitude of the apoptotic switch. Cell culture experiments using siRNA mediated BAX and SMAC knockdowns this model prediction. We further validated the model on data of the NCI-60 cell line panel using BAX protein expression as cell-line specific parameter and show that model simulations correlated with the cellular response to DNA damaging drugs and established a defined threshold for caspase activation that could distinguish between sensitive and resistant melanoma cells. In summary, we present an experimentally validated dynamic model that summarises our current knowledge of how BAX and SMAC regulate the bistable properties of irreversible caspase activation during apoptosis.

systems biology↗

bioRxiv2018

Myc stimulates cell cycle progression through the activation of Cdk1 and phosphorylation of p27

Cell cycle stimulation is a major transforming mechanism of Myc oncoprotein. This is achieved through at least three concomitant mechanisms: upregulation of cyclins and Cdks, downregulation of Cdk inhibitors p15 and p21 and the degradation of p27. The Myc-p27 antagonism has been shown to be relevant in human cancer. To be degraded, p27 must be phosphorylated at Thr-187 to be recognized by Skp2, a component of the ubiquitination complex. We previously described that Myc induces Skp2 expression. Here we show that not only Cdk2 but Cdk1 phosphorylates p27 at the Thr187, which was previously unreported. Moreover, Myc induced p27 degradation in murine fibroblasts through Cdk1 activation, which was achieved by Myc-dependent cyclin A and B induction. In the absence of Cdk2, p27 phosphorylation at Thr-187 was mainly carried out by cyclin A2-Cdk1 and cyclin B1-Cdk1. We also show that Cdk1 inhibition was sufficient for the synthetic lethal interaction with Myc. This result is relevant because Cdk1 is the only Cdk strictly required for cell cycle and the reported synthetic lethal interaction between Cdk1 and Myc.\n\nSummary blurbMyc antagonizes p27 activity in cancer. Myc activates Cdk1 to phosphorylate p27, marking p27 for degradation. This depends on Myc-mediated cyclin A and B induction. Cdk1 inhibition is sufficient for a synthetic lethal interaction with Myc

cancer biology↗