Biology subjects

Moorthi, S.

Publications and source records attributed to Moorthi, S..

6 recordsLinked to original sources

bioRxiv2025

Regulation of cell cycle by the novel GATA1/TAL1/Sphingomyelin Synthase 1 (SGMS1) transcriptional axis. Implications for anti-leukemic strategies.

Sphingomyelin Synthase 1 (gene name: SGMS1) participates in regulation of sphingolipid levels by synthesizing sphingomyelin from ceramide and phosphatidylcholine. Evidence have supported SGMS1s functions in regulating proliferation, cell cycle, cell death and migration. While its functions have begun to be explored, very little is known about upstream regulators. Here, we demonstrate that SGMS1 is a direct gene target of the GATA1-TAL1 transcriptional complex in K562 erythroleukemic cells. A predicted GATA1 consensus DNA binding sequence was identified with in a newly characterized alternative SGMS1 promoter (TSS-7 promoter) and ChIP analysis confirmed GATA1 occupancy on the promoter. Down-regulation of GATA1 in K562 cells significantly decreased SGMS1 expression and enzymatic activity, and ChIP-Seq analysis from ENCODE showed colocalized peaks for GATA1 and TAL1 (a well-established GATA1 DNA binding partner) on the SGMS1 gene. Analysis of publicly available datasets shows that elevated GATA1, TAL1 and SGMS1 expression not only clusters GATA1 positive chronic myelogenous leukemia cells (like K562), but also selectively identifies acute erythrocytic and megakaryocytic leukemias (M6 and M7 AML, respectively). Microarray gene expression analysis after down-regulation of SGMS1 in M6 AML Hel cells revealed alteration of genes regulating G2/M check point and mitotic spindle formation. This phenotype was functionally confirmed by the significant delay in G2/M cell cycle progression of cells with SGMS1 downregulation and sensitization to the clinically relevant anti-mitotic agent, Taxol. Altogether, these results identify SGMS1 as a novel target of GATA1/TAL1 transcriptional complex and they support a role for the GATA1/TAL1/SGMS1 axis in regulating transit through G2/M. Importantly, results also point to combination of anti-mitotic agents and inhibition of SGMS1 as a potential novel therapeutic approach against the aggressive and resilient M6 AMLs. KEY POINTSO_LIThe Sphingomyelin Synthase 1 gene (SGMS1) is a novel direct target of GATA1 and TAL1. C_LIO_LIHigh SGMS1 levels are associated with high GATA1/TAL1 expression and regulate cell cycle progression through the G2/M checkpoint in GATA1+ erythroleukemic Acute Myeloid Leukemia Hel cells. C_LIO_LIHigh SGMS1 is associated with lower probability of survival of patients with Acute Myeloid Leukemia and down-regulation of SGMS1 co-operates with microtubule targeting agents to induce cytotoxicity in GATA1 positive AML Hel cells. C_LI

cancer biology↗

bioRxiv2024

Mutant RIT1 cooperates with YAP to drive an EMT-like lung cancer state

The discovery of oncogene addiction in cancer has led to the development of over a dozen FDA-approved biomarker-driven therapies in lung adenocarcinoma. Somatic mutations of the "Ras-like in all tissues" (RIT1) gene are non-canonical driver events in lung cancer, occurring in [~]2% of lung adenocarcinomas in a mutually exclusive fashion with KRAS and EGFR mutations. Patients with RIT1-mutant lung cancer lack targeted therapy treatment options, and a lack of pre-clinical models has hindered the development of therapeutic strategies for RIT1-mutant lung cancer. Here we report a new mouse model of RIT1-driven lung cancer in which the human RIT1M90I variant can be induced in a Cre-regulated manner. We show that autochthonous expression of RIT1M90I in the lung weakly promotes cancer alone or in combination with loss of the p53 tumor suppressor. However, potent synergy between RIT1M90I and inactivation of Nf2 drives an aggressive epithelial-to-mesenchymal (EMT) lung cancer with 100% penetrance and short latency. We show this oncogenic cooperation is driven by synergistic activation of cJUN, a component of the AP-1 complex. Therapeutic inhibition of MEK and YAP/TEAD suppressed RIT1-driven lung cancer in vivo. These data identify YAP/TEAD as an important mediator of RIT1s oncogenic potential and nominate TEAD as an important drug target in RIT1-mutant lung cancer. HIGHLIGHTSO_LIWe report a new RIT1M90I-mutant autochthonous lung tumor model C_LIO_LIThe most common oncogenic variant of RIT1, RIT1M90I, weakly promotes lung tumor development C_LIO_LIRIT1M90I drives the formation of lethal lung tumors in cooperation with p53 and Nf2 tumor suppressor gene loss C_LIO_LIRIT1M90I and YAP cooperatively regulate cJUN expression C_LIO_LITherapeutic MEK and TEAD targeting suppresses RIT1M90I-driven tumorigenesis C_LI

cancer biology↗

bioRxiv2023

The deubiquitinase USP9X regulates RIT1 protein abundance and oncogenic phenotypes

RIT1 is a rare and understudied oncogene in lung cancer. Despite structural similarity to other RAS GTPase proteins such as KRAS, oncogenic RIT1 activity does not appear to be tightly regulated by nucleotide exchange or hydrolysis. Instead, there is a growing understanding that the protein abundance of RIT1 is important for its regulation and function. We previously identified the deubiquitinase USP9X as a RIT1 dependency in RIT1-mutant cells. Here, we demonstrate that both wild-type and mutant forms of RIT1 are substrates of USP9X. Depletion of USP9X leads to decreased RIT1 protein stability and abundance and resensitizes cells to EGFR tyrosine kinase inhibitors. Our work expands upon the current understanding of RIT1 protein regulation and presents USP9X as a key regulator of RIT1-driven oncogenic phenotypes.

cancer biology↗

bioRxiv2023

Fending for oneself or partnering up: Competition between mixo- and heterotrophic ciliates under dynamic resource supply

The outcome of species competition strongly depends on the traits of the competitors and associated trade-offs, as well as on environmental variability. Here we investigate the relevance of consumer trait variation for species coexistence in a ciliate consumer - microalgal prey system under fluctuating regimes of resource supply. We focus on consumer competition and feeding traits, and specifically on the consumers ability to overcome periods of resource limitation by mixotrophy, i.e. the ability of photosynthetic carbon fixation via algal symbionts in addition to phagotrophy. In a 48-day chemostat experiment, we investigated competitive interactions of different heterotrophic and mixotrophic ciliates of the genera Euplotes and Coleps under different resource regimes, providing prey either continuously or in pulses under constant or fluctuating light, entailing periods of resource depletion in fluctuating environments, but overall providing the same amount of prey and light. Although ultimate competition results remained unaffected, population dynamics of mixotrophic and heterotrophic ciliates were significantly altered by resource supply mode. However, the effects differed among species combinations and changed over time. Whether mixotrophs or heterotrophs dominated in competition strongly depended on the genera of the competing species and thus species-specific differences in the minimum resource requirements that are associated with feeding on shared prey, nutrient uptake, light harvesting and access to additional resources such as bacteria. Potential differences in the curvature of the species resource-dependent growth functions may have further mediated the species-specific responses to the different resource supply modes. In addition, while the presence of a heterotrophic competitor may have a direct negative effect on the growth rate of a mixotrophic species through grazing on a shared prey species, its presence may also have an indirect positive effect on the growth rate of the mixotroph by reducing competition between the autotroph and mixotroph for shared nutrients and light. Our study thus demonstrates that complex trophic interactions determine the outcome of competition, which can only be understood by taking on a multidimensional trait perspective.

ecology↗

bioRxiv2023

Somatic mutation but not aneuploidy differentiates lung cancer in never-smokers and smokers.

Lung cancer in never-smokers disproportionately affects older women. To understand the mutational landscape of this cohort, we performed detailed genome characterization of 73 lung adenocarcinomas from participants of the Womens Health Initiative (WHI). We find enrichment of EGFR mutations in never-/light-smokers and KRAS mutations in heavy smokers as expected, but we also show that the specific variants of these genes differ by smoking status, with important therapeutic implications. Mutational signature analysis revealed signatures of clock, APOBEC, and DNA repair deficiency in never-/light-smokers; however, the mutational load of these signatures did not differ significantly from those found in smokers. Last, tumors from both smokers and never-/light-smokers shared copy number subtypes, with no significant differences in aneuploidy. Thus, the genomic landscape of lung cancer in never-/light-smokers and smokers is predominantly differentiated by somatic mutations and not copy number alterations.

genomics↗

bioRxiv2020

Mapping the unique and shared functions of oncogenic KRAS and RIT1 with proteome and transcriptome profiling

Aberrant activation of RAS oncogenes is prevalent in lung adenocarcinoma, with somatic mutation of KRAS occurring in [~]30% of tumors. Recently, we identified somatic mutation of the RAS-family GTPase RIT1 in lung adenocarcinoma, but relatively little is known about the biological pathways regulated by RIT1 and how these relate to the oncogenic KRAS network. Here we present quantitative proteomic and transcriptomic profiles from KRAS-mutant and RIT1-mutant isogenic lung epithelial cells and globally characterize the signaling networks regulated by each oncogene. We find that both mutant KRAS and mutant RIT1 promote S6 kinase, AKT, and RAF/MEK signaling, and promote epithelial-to-mesenchymal transition and immune evasion via HLA protein loss. However, KRAS and RIT1 diverge in regulation of phosphorylation sites on EGFR, USO1, and AHNAK proteins. The majority of the proteome changes are related to altered transcriptional regulation, but a small subset of proteins are differentially regulated by both oncoproteins at the post-transcriptional level, including intermediate filament proteins, metallothioneins, and MHC Class I proteins. These data provide the first global, unbiased characterization of oncogenic RIT1 network and identify the shared and divergent functions of oncogenic RIT1 and KRAS GTPases in lung cancer.

cancer biology↗