Biology subjects

Mock, B. A.

Publications and source records attributed to Mock, B. A..

6 recordsLinked to original sources

bioRxiv2026

Stability of c-Myc protein differentiates Ras oncogene addiction and MAPK pathway dependency in Ras-mutant multiple myeloma

Multiple myeloma (MM) is a plasma cell malignancy that frequently harbors activating mutations in NRAS and KRAS oncogenes. Previous clinical trials targeting the Ras/MAPK oncogenic pathway with MEK inhibitors (MEKi) were met with limited efficacy, and newer generation of Ras inhibitors (RASi) have not been specifically evaluated in MM patients. To investigate the vulnerabilities of Ras-mutant MM to targeted therapies, we examined the sensitivity of a panel of human MM cell lines to the RASi RMC-6236 (daraxonrasib) and the MEKi trametinib. Although Ras-mutant MM cells are responsive to oncogenic Ras signaling and are sensitive to RAS inhibition, their sensitivity to MEK inhibition is heterogeneous. Mechanistic studies revealed that c-Myc protein is destabilized by MEK inhibition only in MEKi-sensitive MM cells but not in MEKi-resistant cells, and pharmacological and genetic stabilization of c-Myc is sufficient to confer MEKi resistance. In contrast, Ras inhibition reduced c-Myc protein across all MM cell lines tested, regardless of their dependency on the MAPK pathway, and c-Myc expression was insufficient to promote RASi resistance. Together, these findings demonstrate that c-Myc protein stability differentiates the response of Ras-mutant MM cells to Ras and MEK inhibition, and suggest that direct targeting of the Ras oncoprotein, rather than its downstream MAPK pathway, may present a more effective strategy.

cancer biology↗

bioRxiv2025

Capacity for compensatory cyclin D2 response confers trametinib resistance in canine mucosal melanoma

Background/objectiveMucosal melanoma (MM) is a poorly responsive, rare and aggressive subtype with paucity of targetable recurrent driver mutations, although Ras/MAPK and PI3K/AKT/mTOR signaling pathway activations are common. Eventual tumor evasion of targeted therapy continues to limit treatment success. Adequate models are necessary to address therapeutic resistance. The relatively greater incidence of naturally occurring MM in dogs, as well as its comparable clinical and pathological characteristics to human MM, represents a promising opportunity for predictive patient modeling. Resistance-promoting crosstalk between Ras/MAPK and PI3K/AKT/mTOR signaling under trametinib inhibition of MEK was studied in a canine MM model. Emphasis was placed on the suppressive effect of trametinib on cell cycle entry and its potential role in drug resistance. MethodsD-type cyclins were investigated using five MM cell lines exhibiting differential sensitivities to trametinib. Drug-treated cells were analyzed for signaling pathway activation, proliferation, survival, cell death, and cell cycle in the context of D-type cyclin expression. Cyclin D2 expression was manipulated using siRNA knock down or inducible recombinant overexpression. ResultsWith diminished cyclin D1 under trametinib treatment, relatively trametinib-resistant MM cells exhibited capacity to upregulate cyclin D2, which promoted proliferation, whereas sensitive cells did not similarly respond. Inhibition of the compensatory cyclin D2 response restored sensitivity to resistant cells. Induced cyclin D2 overexpression promoted survival to otherwise trametinib-sensitive MM cells that did not exhibit capacity to upregulate endogenous cyclin D2. PI3K/AKT/mTOR signaling upregulation under trametinib was suppressed by mTORC1/2 inhibition, which similarly diminished cyclin D2 response. ConclusionThe compensatory switch from preferential reliance on cyclin D1 to D2 appears to play a role in MM resistance to MEK inhibition.

cancer biology↗

bioRxiv2025

Topoisomerase IIIb protects from tumorigenesis and immune dysregulation

Topoisomerase III-beta (Top3b) reduces nucleic acid torsional stress and intertwining generated during RNA and DNA metabolism while protecting the genome from pathological R-loops, which otherwise result in DNA breakage and genome instability. By studying Top3b knockout mice (Top3b-KO), we find that the loss of Top3b accelerates the development of spontaneous lymphoid tumors arising in spleens and lymph nodes, the organs with prominent Top3b expression. Aging Top3b-KO mice also display splenomegaly and systemic immune alterations including neutrophilia and lymphopenia suggestive of chronic inflammation. At the molecular level, Top3b deficiency causes genome-wide R-loop accumulation in splenocytes as measured by CUT&Tag sequencing. Increased R-loops is associated with genomic DNA breaks and activation of immune signaling pathways including the IL-6 signaling, interleukin-7 signaling and cGAS-STING. Moreover, knocking-out Top3b promotes the rapid development of syngeneic EL4 T-cell lymphomas. In conclusion, our work implies that, in addition to its role in preserving the nervous system, Top3b protects from tumorigenesis and immune dysregulations. SignificanceTopoisomerase III-beta (TOP3B) is the only dual RNA-DNA topoisomerase. Its inactivation has previously been shown to be critical for neurodevelopmental disorders in humans and R-loop suppression in cell line models. Here, we demonstrate that loss of Top3b accelerates spontaneous lymphomagenesis and promotes syngeneic lymphoma growth in association with innate immune defects and R-loop accumulation in Top3b-KO mice. These findings provide evidence for a previously unappreciated role of Top3b as a tumor suppressor gene and immune regulator.

cancer biology↗

bioRxiv2024

Transfer RNA acetylation regulates in vivo mammalian stress signaling

Transfer RNA (tRNA) modifications are crucial for protein synthesis, but their position-specific physiological roles remain poorly understood. Here we investigate the impact of N4-acetylcytidine (ac4C), a highly conserved tRNA modification, using a Thumpd1 knockout mouse model. We find that loss of Thumpd1-dependent tRNA acetylation leads to reduced levels of tRNALeu, increased ribosome stalling, and activation of eIF2 phosphorylation. Thumpd1 knockout mice exhibit growth defects and sterility. Remarkably, concurrent knockout of Thumpd1 and the stress-sensing kinase Gcn2 causes penetrant postnatal lethality, indicating a critical genetic interaction. Our findings demonstrate that a modification restricted to a single position within type II cytosolic tRNAs can regulate ribosome-mediated stress signaling in mammalian organisms, with implications for our understanding of translation control as well as therapeutic interventions.

developmental biology↗

bioRxiv2022

Deep Phenotyping and Lifetime Trajectories Reveal Limited Effects of Longevity Regulators on the Aging Process in C57BL/6J Mice

Current concepts regarding the biology of aging are based on studies aimed at identifying factors regulating natural lifespan. However, lifespan as a sole proxy measure for aging can be of limited value because it may be restricted by specific sets of pathologies, rather than by general physiological decline. Here, we employed large-scale phenotyping to analyze hundreds of phenotypes and thousands of molecular markers across tissues and organ systems in a single study of aging male C57BL/6J mice. For each phenotype, we established lifetime profiles to determine when age-dependent phenotypic change is first detectable relative to the young adult baseline. We examined central genetic and environmental lifespan regulators (putative anti-aging interventions, PAAIs; the following PAAIs were examined: mTOR loss-of-function, loss-of-function in growth hormone signaling, dietary restriction) for a possible countering of the signs and symptoms of aging. Importantly, in our study design, we included young treated groups of animals, subjected to PAAIs prior to the onset of detectable age-dependent phenotypic change. In parallel to our studies in mice, we assessed genetic variants for their effects on age-sensitive phenotypes in humans. We observed that, surprisingly, many PAAI effects influenced phenotypes long before the onset of detectable age-dependent changes, rather than altering the rate at which these phenotypes developed with age. Accordingly, this subset of PAAI effects does not reflect a targeting of age-dependent phenotypic change. Overall, our findings suggest that comprehensive phenotyping, including the controls built in our study, is critical for the investigation of PAAIs as it facilitates the proper interpretation of the mechanistic mode by which PAAIs influence biological aging. HighlightsO_LIPhenotyping at scale defines lifetime trajectories of age-dependent changes in C57BL/6J mice C_LIO_LICentral genetic and environmental lifespan regulators (putative anti-aging interventions; PAAIs) influence age-sensitive phenotypes (ASPs) often long before the appearance of age-dependent changes in these ASPs C_LIO_LICorresponding genetic variants in humans also have age-independent effects C_LIO_LIMany PAAI effects shift the baseline of ASPs rather than slowing their rate of change C_LI

physiology↗

bioRxiv2021

mTOR Inhibition Overcomes RSK3-mediated Resistance to BET Inhibitors in Small Cell Lung Cancer

PurposeSCLC is a recalcitrant malignancy with limited treatment options. BET inhibitors have shown promising preclinical activity in SCLC, but their broad sensitivity spectrum limits their clinical prospects in this malignancy. Drug combination could be a solution. Experimental designWe performed high-throughput drug combination screens in SCLC cell lines to identify potential therapeutics synergizing with BET inhibitors. Validation was performed in SCLC cell lines and patient-derived xenograft models. Genome-wide RNA sequencing of xenograft tumors was performed to determine the mechanism underlying the synergy of the drug combination. ResultsInhibitors of the PI-3K-AKT-mTOR pathway were the top candidates from the screens. Among the therapeutics targeting this pathway, mTOR inhibitors showed the highest degree of synergy with BET inhibitors in vitro. Furthermore, the combination of these two classes of drugs showed superior antitumor efficacy and tolerability in vivo. Using both in vitro and in vivo SCLC models, we demonstrate that BET inhibitors activate the intrinsic apoptotic cascade, and mTOR inhibitors further enhance these apoptotic effects. Mechanistically, BET inhibitors activate the TSC2-mTOR-p70S6K1 signaling cascade by upregulating RSK3, an upstream kinase of TSC2. Activation of p70S6K1 leads to BAD phosphorylation and cell survival. mTOR inhibition blocks this survival signaling cascade and potentiates the antitumor effects of BET inhibitors. ConclusionsOur results demonstrate that RSK3 upregulation is a novel resistance mechanism of BET inhibitors in SCLC, and mTOR inhibition can overcome this resistance and enhance apoptosis. These findings provide a rationale to evaluate the combination of mTOR and BET inhibitors in patients with SCLC.

cancer biology↗