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Mutational blows to Sox2+ cells induce epithelial squamous tumor initiation

ABSTRACT: Cancer originates as the progressive accumulation of genetic mutations in proto-oncogenes and tumor suppressors. However, the early events underlying tumor initiation remain largely elusive, mostly due to the general lack of information regarding the cells-of-origin responsible for tumor formation as well as the precise impacts of genetic insults on tumor initiation in vivo. Here, we demonstrate that Sox2-positive (Sox2+) adult stem cells are responsible for epithelial squamous tumor formation. Conditional expression of oncogenic Kras (KrasG12D) and knockout of p53 (also known as Trp53) in Sox2+ cells quickly and specifically resulted in the formation of squamous tumors in the forestomach and esophagus. GFP-based lineage tracing experiments demonstrated that Sox2+ cells are the cells-of-origin of squamous tumors in the esophagus and forestomach. Of note, our data showed that p53 deletion alone did not suffice for tumor initiation. On the contrary, tumor initiation was observed upon KrasG12D activation whereas p53 deletion further contributed to the malignancy of the generated tumors, pointing out distinct roles for Kras activation and p53 deletion in squamous tumor formation and progression, to which a multihit carcinogenesis model can be applied. Global gene expression analysis revealed secreting factors upregulated in the generated tumors induced by oncogenic Kras, which contribute to tumor progression. Taken together, these results demonstrate that epithelial squamous tumors can specifically originate as a consequence of defined genetic mutations in a Sox2+ cell population and highlight the connections between proliferative stem cells and tumor development in vivo.

ORGANISM(S): Mus musculus

PROVIDER: GSE66457 | GEO | 2017/01/01

SECONDARY ACCESSION(S): PRJNA277009

REPOSITORIES: GEO

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Project description:The maintenance of advanced malignancies relies on continued activity of driver oncogenes, although their rate-limiting role is highly context-dependent with respect to tumor types and associated genetic alterations. Oncogenic Kras mutation is the signature event in human pancreatic ductal adenocarcinoma (PDAC), serving a critical role in tumor initiation. Here, an inducible KrasG12D-driven p53 mutant PDAC mouse model establishes that advanced PDAC remains strictly dependent on continued KrasG12D expression and that KrasG12D serves a vital role in the control of tumor metabolism, through stimulation of glucose uptake and channeling of glucose intermediates through the hexosamine biosynthesis pathway (HBP) and the pentose phosphate pathway (PPP). Notably, these studies reveal that oncogenic Kras regulates ribose biogenesis. Unlike canonical models of PPP-mediated ribose biogenesis, we demonstrate that oncogenic Kras drives intermediates from enhanced glycolytic flux into the non-oxidative arm of the PPP, thereby decoupling ribose biogenesis from NADPNADPH-mediated redox control. Together, this work provides in vivo mechanistic insights into how oncogenic Kras promotes metabolic reprogramming in native tumors and illuminates potential metabolic targets that can be exploited for therapeutic benefit in Kras-driven PDAC. Primary pancreatic tumor lines were established from p48Cre tetO_LKrasG12D ROSA_rtTAL+ p53L+ mice. Five independent tumor lines (iKras1-5) were used for pancreatic injection into nude mice to generate orthotopic tumors. The mice were kept on doxycycline for 2 weeks until obvious tumor formation. Half of the animals were pulled off doxycycline for 24 hours. Tumors with over 75% cellularity were collected for total RNA prepartion. For in vitro expression profiles, the same five tumor lines were cultured in the presence or absence of doxycycline for 24 hours and total cellular RNA was prepared. For control samples, two independent tumor lines from LSL-KrasG12D p53L+ tumors were cultured in the presence or absence of doxycycline for 24 hours and total cellular RNA was prepared.

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Mutational blows to Sox2+ cells induce epithelial squamous tumor initiation

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