KSR1 regulates small-cell lung carcinoma tumor initiation and therapy resistance.

Small-cell lung cancer (SCLC) is designated a recalcitrant cancer due to its five-year relative survival rate of less than 7%. First line SCLC treatment has not changed in the last 40 years. The NeuroD1 subtype of SCLC (SCLC-N) commonly harbors MYC amplifications and other hallmarks of aggressive behavior. Finding novel therapeutic options that effectively eliminate residual disease observed after initial response to therapy is essential to improving SCLC patient outcome. Tumor-initiating cells (TICs) are reported as the sanctuary population within the bulk tumor responsible for therapeutic resistance and relapse. In contrast to earlier studies in which ERK activation is reported to be inhibitory to growth and tumor development, we show that KSR1 signaling is conserved in SCLC-N and that it regulates tumor initiation through ERK. Thus, KSR1 function in SCLC-N serves as a novel model for understanding the role of KSR1-dependent signaling in normal and malignant tissues. We further show that KSR1 mediates cisplatin resistance in SCLC-N cells. CRISPR/Cas9-mediated KSR1 knockout causes a dramatic increase in sensitivity to cisplatin and is coincident with a marked decrease in TICs, indicating that targeting KSR1 might be selectively toxic to cells responsible for therapeutic resistance and tumor initiation. Our data show that KSR1, a molecular scaffold for the Raf/MEK/ERK signaling cascade, is critical for tumor initiation and clonogenicity, both in vitro and in vivo in the highly aggressive, metastatic and therapy resistant NeuroD1 subtype of SCLC. These findings shed light on a key distinct protein responsible for regulation in SCLC-N tumors, and a potential subtype specific therapeutic target.

SOS1 and KSR1 modulate MEK inhibitor responsiveness to target resistant cell populations based on PI3K and KRAS mutation status.

KRAS is the most commonly mutated oncogene. Targeted therapies have been developed against mediators of key downstream signaling pathways, predominantly components of the RAF/MEK/ERK kinase cascade. Unfortunately, single-agent efficacy of these agents is limited both by intrinsic and acquired resistance. Survival of drug-tolerant persister cells within the heterogeneous tumor population and/or acquired mutations that reactivate receptor tyrosine kinase (RTK)/RAS signaling can lead to outgrowth of tumor-initiating cells (TICs) and drive therapeutic resistance. Here, we show that targeting the key RTK/RAS pathway signaling intermediates SOS1 (Son of Sevenless 1) or KSR1 (Kinase Suppressor of RAS 1) both enhances the efficacy of, and prevents resistance to, the MEK inhibitor trametinib in KRAS-mutated lung (LUAD) and colorectal (COAD) adenocarcinoma cell lines depending on the specific mutational landscape. The SOS1 inhibitor BI-3406 enhanced the efficacy of trametinib and prevented trametinib resistance by targeting spheroid-initiating cells in KRASG12/G13-mutated LUAD and COAD cell lines that lacked PIK3CA comutations. Cell lines with KRASQ61 and/or PIK3CA mutations were insensitive to trametinib and BI-3406 combination therapy. In contrast, deletion of the RAF/MEK/ERK scaffold protein KSR1 prevented drug-induced SIC upregulation and restored trametinib sensitivity across all tested KRAS mutant cell lines in both PIK3CA-mutated and PIK3CA wild-type cancers. Our findings demonstrate that vertical inhibition of RTK/RAS signaling is an effective strategy to prevent therapeutic resistance in KRAS-mutated cancers, but therapeutic efficacy is dependent on both the specific KRAS mutant and underlying comutations. Thus, selection of optimal therapeutic combinations in KRAS-mutated cancers will require a detailed understanding of functional dependencies imposed by allele-specific KRAS mutations.

Splice-altering variant in COL11A1 as a cause of nonsyndromic hearing loss DFNA37.

PURPOSE: The aim of this study was to determine the genetic cause of autosomal dominant nonsyndromic hearing loss segregating in a multigenerational family. METHODS: Clinical examination, genome-wide linkage analysis, and exome sequencing were carried out on the family. RESULTS: Affected individuals presented with early-onset progressive mild hearing impairment with a fairly flat, gently downsloping or U-shaped audiogram configuration. Detailed clinical examination excluded any additional symptoms. Linkage analysis detected an interval on chromosome 1p21 with a logarithm of the odds (LOD) score of 8.29: designated locus DFNA37. Exome sequencing identified a novel canonical acceptor splice-site variant c.652-2A>C in the COL11A1 gene within the DFNA37 locus. Genotyping of all 48 family members confirmed segregation of this variant with the deafness phenotype in the extended family. The c.652-2A>C variant is novel, highly conserved, and confirmed in vitro to alter RNA splicing. CONCLUSION: We have identified COL11A1 as the gene responsible for deafness at the DFNA37 locus. Previously, COL11A1 was solely associated with Marshall and Stickler syndromes. This study expands its phenotypic spectrum to include nonsyndromic deafness. The implications of this discovery are valuable in the clinical diagnosis, prognosis, and treatment of patients with COL11A1 pathogenic variants.

Searching for evidence of DFNB2.

Deafness is the most common form of sensory impairment in humans, affecting about 1 in 1,000 births in the United States. Of those cases with genetic etiology, approximately 80% are nonsyndromic and recessively inherited. Mutations in several unconventional myosins, members of a large superfamily of actin-associated molecular motors, have been found to cause hearing loss in both humans and mice. Mutations in the human unconventional Myosin VIIa (MYO7A), located at 11q13.5, are reported to be responsible for both syndromic and nonsyndromic deafness. MYO7A mutations are responsible for Usher syndrome type Ib, the most common genetic subtype of Usher I. Usher I is clinically characterized by congenital profound deafness, progressive retinal degeneration called retinitis pigmentosa (RP), and vestibular areflexia. Although a wide spectrum of MYO7A mutations have been identified in Usher Ib patients, four mutations have been reported to cause DFNB2, a recessive deafness without retinal degeneration, and one mutation has been implicated in a single case of dominant nonsyndromic hearing loss (DFNA11). Our study attempts to ascertain additional DFNB2 families to investigate the disparate nonsyndromic phenotype and alleged causative mutations. Data from both linkage and heterogeneity analyses on 36 selected autosomal recessive nonsyndromic deafness (RNSD) families, all previously excluded by mutational analysis from GJB2 (Cx26), the leading cause of nonsyndromic deafness, showed no evidence of DFNB2 within the sample. These negative results and the isolated reports of DFNB2 bring into question whether certain MYO7A mutations produce nonsyndromic recessive hearing loss.