Maribel Espitia

Large-scale sequencing efforts are uncovering the complexity of cancer genomes, which are composed of causal "driver" mutations that promote tumor progression along with many more pathologically neutral "passenger" events. The majority of mutations, both in known cancer drivers and uncharacterized genes, are generally of low occurrence, highlighting the need to functionally annotate the long tail of infrequent mutations present in heterogeneous cancers. Here we describe a mutation assessment pipeline enabled by high-throughput engineering of molecularly barcoded gene variant expression clones identified by tumor sequencing. We first used this platform to functionally assess tail mutations observed in PIK3CA, which encodes the catalytic subunit alpha of the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) frequently mutated in cancer. Orthogonal screening for PIK3CA variant activity using in vitro and in vivo cell growth and transformation assays differentiated driver from passenger mutations, revealing that PIK3CA variant activity correlates imperfectly with its mutation frequency across breast cancer populations. Although PIK3CA mutations with frequencies above 5% were significantly more oncogenic than wild-type in all assays, mutations occurring at 0.07% to 5.0% included those with and without oncogenic activities that ranged from weak to strong in at least one assay. Proteomic profiling coupled with therapeutic sensitivity assays on PIK3CA variant-expressing cell models revealed variant-specific activation of PI3K signaling as well as other pathways that include the MEK1/2 module of mitogen-activated protein kinase pathway. Our data indicate that cancer treatments will need to increasingly consider the functional relevance of specific mutations in driver genes rather than considering all mutations in drivers as equivalent.

As we enter the era of precision medicine, characterization of cancer genomes will directly influence therapeutic decisions in the clinic. Here we describe a platform enabling functionalization of rare gene mutations through their high-throughput construction, molecular barcoding and delivery to cancer models for in vivo tumour driver screens. We apply these technologies to identify oncogenic drivers of pancreatic ductal adenocarcinoma (PDAC). This approach reveals oncogenic activity for rare gene aberrations in genes including NAD Kinase (NADK), which regulates NADP(H) homeostasis and cellular redox state. We further validate mutant NADK, whose expression provides gain-of-function enzymatic activity leading to a reduction in cellular reactive oxygen species and tumorigenesis, and show that depletion of wild-type NADK in PDAC cell lines attenuates cancer cell growth in vitro and in vivo. These data indicate that annotating rare aberrations can reveal important cancer signalling pathways representing additional therapeutic targets.

Human leucocyte antigen (HLA) B*27 is a susceptibility allele to ankylosing spondylitis (AS). However, major AS-associated subtypes of HLA-B*27 and other HLA-B alleles vary in different ethnic populations. Herein, we examined HLA-B alleles in a total of 360 AS patients and 350 controls of Chinese Han ancestry. The HLA-B genotyping was performed with sequence-based typing (SBT) method. Six HLA-B*27 subtypes B*27:04, B*27:05, B*27:07, B*27:08, B*27:10 and B*27:15 were observed in the cohorts. HLA-B*27:04:01 and -B*27:05:02 appeared significantly increased in AS patients, which indicated as two major susceptibility alleles to AS. Homozygous B*27 was observed only in AS patients. There are 30 HLA-B alleles identified in the studies. HLA-B*15, especially B*15:01:01:01, appeared as the major allele type in the Chinese controls. Some common HLA-B alleles such as HLA-B*15, B*13, B*46 and B*51 were significantly reduced in Chinese AS patients. In conclusion, the studies profiled the HLA-B alleles, and identified major susceptibility subtypes of B27 to AS in Han Chinese population

Objective. Findings from previous genome-wide association studies indicated an association of the NOTCH4 gene with systemic sclerosis (SSc). This is a followup study to fine-map exonic variants of NOTCH4 in SSc. Methods. All exons of NOTCH4 were sequenced and analyzed in a total of 1006 patients with SSc and 1004 controls of US white ancestry with the Ion Torrent system. Identified SSc-associated variants were confirmed with Sanger sequencing, and then examined in a Chinese Han cohort consisting of 576 patients with SSc and 574 controls. The NOTCH4 variants were analyzed for association with SSc as a whole and with SSc clinical and autoantibody subtypes with and without the influence of specific HLA-class II alleles that had been previously identified as major genetic factors in SSc. Results. A total of 12 SSc-associated and SSc subtype–associated exonic variants of NOTCH4 were identified in the US cohort. Three of them are nonsynonymous single-nucleotide polymorphisms and 1 is a CTG tandem repeat that encodes for a poly-leucine, all of which are located in the NOTCH4 extracellular domain (NECD). Conditional logistic regression analysis on SSc-associated HLA-class II alleles indicated an independent association of the NOTCH4 variants with SSc autoantibody subtypes. Analysis of the Chinese cohort supported a genetic contribution of NOTCH4 to SSc and its subtypes. Conclusion. Multiple NOTCH4 exonic variants were associated with SSc and/or SSc subtypes. Several of these variants encode nonsynonymous sequence changes occurring in the NECD, which implicates a potentially functional effect of NOTCH4 .