Project description:The kinase LKB1 is a critical tumor suppressor in sporadic and familial human cancers, yet the mechanisms by which it suppresses tumor growth remain poorly understood. To investigate the tumor-suppressive capacity of four canonical families of LKB1 substrates in vivo, we used CRISPR/Cas9-mediated combinatorial genome editing in a mouse model of oncogenic KRAS-driven lung adenocarcinoma. We demonstrate that members of the SIK family are critical for constraining tumor development. Histologic and gene-expression similarities between LKB1- and SIK-deficient tumors suggest that SIKs and LKB1 operate within the same axis. Furthermore, a gene-expression signature reflecting SIK deficiency is enriched in LKB1-mutant human lung adenocarcinomas and is regulated by LKB1 in human cancer cell lines. Together, these findings reveal a key LKB1-SIK tumor-suppressive axis and underscore the need to redirect efforts to elucidate the mechanisms through which LKB1 mediates tumor suppression. SIGNIFICANCE: Uncovering the effectors of frequently altered tumor suppressor genes is critical for understanding the fundamental driving forces of cancer growth. Our identification of the SIK family of kinases as effectors of LKB1-mediated tumor suppression will refocus future mechanistic studies and may lead to new avenues for genotype-specific therapeutic interventions.This article is highlighted in the In This Issue feature, p. 1469.
Project description:Background: LKB1 is among the most frequently altered tumor suppressors in lung adenocarcinoma. Despite being implicated in the regulation of a variety of cellular processes, the mechanisms by which LKB1 constrains lung tumor growth and progression remains an area of intense investigation. Purpose: To determine the extent of overlap in terms of the transcriptomic states arising from either Lkb1 deletion or Sik-targeting within cancer cells isolated from genetically engineered mouse models of oncogenic Kras-driven lung adenocarcinoma Approach: Cancer cells sorted from mouse lung tumors of defined genotypes were profiled by RNA-seq. Results: A strong overlap existed between Lkb1-deficient and Sik-targeted cancer cells both at the gene and pathways levels. Conclusions: Given the strong transcriptional overlap, loss of either Lkb1 or Sik appear to be functionally related.
Project description:Background: LKB1 is among the most frequently altered tumor suppressors in lung adenocarcinoma. Despite being implicated in the regulation of a variety of cellular processes, the mechanisms by which LKB1 constrains lung tumor growth and progression remains an area of intense investigation. Purpose: To assess the impact of CRISPR/Cas9-mediated targeting of the canonical substrates of Lkb1 on tumor size within the context of a genetically engineered mouse model of oncogenic Kras-driven lung adenocarcinoma. Approach: Comparisons of tumor size across genetic perturbations were conducting by measuring tumor sizes via tumor barcode sequencing (Rogers, et al. 2017 Nature Methods). Briefly, tumors were initiated in KrasLSL-G12D/+;R26LSL-Tomato, KrasLSL-G12D/+;Lkb1flox/flox;R26LSL-Tomato;H11LSL-Cas9, and KrasLSL-G12D/+;R26LSL-Tomato;H11LSL-Cas9 mice using a pool of Lenti-sgRNA/Cre vectors that encode a cassette comprised of an sgRNA-specific ID along with clonal identifier. Following, tumor development/progression, the two-component lentiviral cassettes integrated within transduced populations were amplified from genomic DNA extracted from whole lungs homogenates and subjected to next-generation sequencing. From the resulting reads, barcode pileups were generated and filtered prior to translation to absolute numbers of cancer cells via normalization to spiked-in samples of known quantities of cancer cells. The resultant tumor size distribution were then analyzed by multiple statistical measures as described by Rogers, et al. Results: Lkb1 targeting dramatically increased tumor size in the Kras-only setting relative to functionally inert sgRNAs. Unlike other families of Lkb1 substrates, the targeting of the salt inducible kinase (Sik) family increased tumor growth comparable to Lkb1 targeting. In contrast to targeting the paralogs Sik1 and Sik3 individually, dual targeting of Sik1 and Sik3 enhanced tumor growth. Sik targeting in the Lkb1-deficient setting also modestly increased tumor size whereas Lkb1 targeting had no effect. Conclusions: Siks are potent tumor suppressors belonging the family of canonical Lkb1 substrates. Siks retain some tumor-suppressive activity in the absence of Lkb1.
Project description:The role of STAT2 in mediating the antigrowth effects of type I interferon (IFN) is well-documented in vitro. Yet evidence of IFN-activated STAT2 as having tumor suppressor function in vivo and participation in antitumor immunity is lacking. Here we show in a syngeneic tumor transplantation model that STAT2 reduces tumor growth. Stat2(-/-) mice formed larger tumors compared to wild type (WT) mice. IFN-? treatment of Stat2(-/-) mice did not cause tumor regression. Gene expression analysis revealed a small subset of immunomodulatory genes to be downregulated in tumors established in Stat2(-/-) mice. Additionally, we found tumor antigen cross-presentation by Stat2(-/-) dendritic cells to T cells to be impaired. Adoptive transfer of tumor antigen specific CD8(+) T cells primed by Stat2(-/-) dendritic cells into tumor-bearing Stat2(-/-) mice did not induce tumor regression with IFN-? intervention. We observed that an increase in the number of CD4(+) and CD8(+) T cells in the draining lymph nodes of IFN-?-treated tumor-bearing WT mice was absent in IFN-? treated Stat2(-/-) mice. Thus our study provides evidence for further evaluation of STAT2 function in cancer patients receiving type I IFN based immunotherapy.
Project description:Liver kinase b1 (Lkb1) protein kinase activity regulates cell growth and cell polarity. Here, we show Lkb1 is essential for maintaining a balance between mitotic and postmitotic cell fates in development of the mammalian skeleton. In this process, Lkb1 activity controls the progression of mitotic chondrocytes to a mature, postmitotic hypertrophic fate. Loss of this Lkb1-dependent switch leads to a dramatic expansion of immature chondrocytes and formation of enchondroma-like tumors. Pathway analysis points to a mammalian target of rapamycin complex 1-dependent mechanism that can be partially suppressed by rapamycin treatment. These findings highlight a critical requirement for integration of mammalian target of rapamycin activity into developmental decision-making during mammalian skeletogenesis.