β-catenin/CBP activation of mTORC1 signaling promotes partial epithelial-mesenchymal states in head and neck cancer

Head and neck cancers, which include oral squamous cell carcinoma (OSCC) as a major subsite, exhibit cellular plasticity that includes features of an epithelial-mesenchymal transition (EMT), referred to as partial-EMT (p-EMT). To identify molecular mechanisms contributing to OSCC plasticity, we performed a multiphase analysis of single cell RNA sequencing (scRNAseq) data from human OSCC. This included a multiresolution characterization of cancer cell subgroups to identify pathways and cell states that are heterogeneously represented, followed by casual inference analysis to elucidate activating and inhibitory relationships between these pathways and cell states. This approach revealed signaling networks associated with hierarchical cell state transitions, which notably included an association between β-catenin-driven CREB-binding protein (CBP) activity and mTORC1 signaling. This network was associated with subpopulations of cancer cells that were enriched for markers of the p-EMT state and poor patient survival. Functional analyses revealed that β-catenin/CBP induced mTORC1 activity in part through the transcriptional regulation of a raptor-interacting protein, chaperonin containing TCP1 subunit 5 (CCT5). Inhibition of β-catenin-CBP activity through the use of the orally active small molecule, E7386, reduced the expression of CCT5 and mTORC1 activity in vitro, and inhibited p-EMT-associated markers and tumor development in a murine model of OSCC. Our study highlights the use of multiresolution network analyses of scRNAseq data to identify targetable signals for therapeutic benefit, thus defining an underappreciated association between β-catenin/CBP and mTORC1 signaling in head and neck cancer plasticity.

Genomic structure of SAS, a member of the transmembrane 4 superfamily amplified in human sarcomas

SAS is a recently identified member of the transmembrane 4 superfamily (TM4SF) that is frequently amplified in human sarcomas. To further its characterization and to confirm its classification, the genomic structure of the SAS gene was determined. The SAS gene covers approximately 3.2 kb of DNA. It contains six exons within its translated region, three of which are highly conserved in the TM4SF. 5' to the translation start site are two putative transcription start sites, two CCAAT consensus sequences, and potential binding sites for both Sp1 and ATF transcription factors. Comparison of SAS organization to human ME491, CD9, and CD53 and murine CD53 and TAPA-1 confirms that SAS is a member of this family of genes and is consistent with the theory that these genes arose through duplication and divergent evolution.

SAS, a gene amplified in human sarcomas, encodes a new member of the transmembrane 4 superfamily of proteins

Amplification of 12q13-14 occurs in a subset of human sarcomas including malignant fibrous histiocytoma and liposarcoma. This chromosomal region has previously been found to include a number of growth-related genes including the GLI proto-oncogene and the p53-associated protein, MDM2. We now report the characterization of SAS (sarcoma amplified sequence), a novel transcript found in this region. Sequence analysis demonstrates that SAS is a novel member of a transmembrane protein family (transmembrane 4 superfamily or TM4SF) thought to be involved in growth-related cellular processes. This observation adds a TM4SF protein to the cluster of genes at 12q13-14 frequently amplified in human sarcomas.

Isolation of a yeast artificial chromosome clone that spans the (12;16) translocation breakpoint characteristic of myxoid liposarcoma

Cytogenetic analysis of liposarcomas has demonstrated that translocation (12;16) (q13.3;p11.2) is characteristic of the myxoid subtype of this adipose tissue tumor. Our previous results suggested that the GLI gene is close to the translocation breakpoint on chromosome 12. We now describe a yeast artificial chromosome (YAC) that contains GLI and spans the chromosome 12 region involved in the t(12;16) breakpoint. This clone will permit rapid definition of the genetic region surrounding the breakpoint and allow isolation of the gene presumably affected by the translocation.

SAS amplification in soft tissue sarcomas

Gene amplification is an important mechanism of increased gene expression in a number of human solid tumors. We have recently identified and cloned sequences from a novel DNA amplification unit in malignant fibrous histiocytoma. The amplified sequences are derived from chromosome 12q13-14 and encode a gene designated SAS (sarcoma amplified sequence). In the present study, a series of soft tissue sarcomas was studied to characterize further the phenomenon of SAS amplification. Seven of 22 (32%) malignant fibrous histiocytomas and three liposarcomas contained SAS amplification. Strikingly, all of the tumors with SAS amplification occurred in central sites (i.e., in the abdominal or inguinal regions) rather than in the extremities (i.e., in the arms of legs). These observations demonstrate that SAS amplification occurs with a significant frequency in mesenchymal tumors and is particularly associated with abdominal disease.

Identification and cloning of a novel amplified DNA sequence in human malignant fibrous histiocytoma derived from a region of chromosome 12 frequently rearranged in soft tissue tumors

Amplification of cellular oncogenes occurs frequently in several human cancers and is an important mechanism of increased gene expression. Identification of amplified genes in tumor cells has proved to be a useful approach for understanding genetic alterations in cancer. Previous procedures for isolating probes from amplified DNA sequences have relied on tissue culture cells, limiting the range of tumors that can be studied and raising questions of in vitro artifact. We have circumvented these problems by combining in gel renaturation of amplified sequences with the polymerase chain reaction. Using this approach, we have identified and partially cloned a DNA amplification unit from biopsies of human malignant fibrous histiocytoma. This amplification unit is derived from chromosome 12q13-14, a site commonly involved in rearrangements in soft tissue tumors, and contains at least one transcribed region (designated SAS, for sarcoma amplified sequence).