Melanoma glycome in disease progression (Dimitroff lab)
Metastatic melanoma (MM) has a dismal 5-year survival rate of 25%. Hence, there is dire need for novel biomarkers to predict metastasis and forecast efficacious therapies. My research is aimed at elucidating the metastatic consequences of elevated fetal i-linear glycans and related loss of I-branching enzyme GCNT2 in MM and investigate whether loss of GCNT2 can predict disease progression. Preliminary data indicate that increased expression of i-linear glycans (GCNT2 downregulation) enhances tumor-initiating cell (TIC) generation and increases stem marker CD271 and invasion and colony-forming activities. Further, hypoxia-induced decreases in GCNT2 and differentiation marker MITF and an increase in stem marker KLF4 were observed and implicate GCNT2 as a regulator TIC generation. Additionally, depressed GCNT2 levels corresponded with significantly reduced melanoma patient survival and marked reduction in response to immune checkpoint (ICI) therapy. We, therefore, hypothesize that hypoxia-dependent GCNT2 downregulation drive MM immune evasion and disease progression. Utilizing genetically-engineered mouse (GEM) models of MM and GCNT2 gene regulation methods in patient-derived MM organoids will allow for analysis of GCNT2 downregulation in melanoma progression and ICI therapy resistance. In all, my research will underscore development of new biomarkers for MM and unveil how MM glycome can be therapeutically targeted to boost ICI therapy.
Galectins and immune modulation (Dimitroff lab)
Humoral immunity is reliant on efficient recruitment of circulating naïve B cells from blood into peripheral lymph nodes (LN) and timely transition of naïve B cells to high affinity antibody (Ab)-producing cells. Current understanding of factor(s) coordinating B cell adhesion, activation and differentiation within LN, however, is incomplete. Prior studies on naïve B cells reveal remarkably strong binding to putative immunoregulator, galectin (Gal)-9, that attenuates BCR activation and signaling, implicating Gal-9 as a negative regulator in B cell biology. My recent publication investigated Gal-9 localization in human tonsils and LNs and unearthed conspicuously high expression of Gal-9 on high endothelial and post-capillary venules. Adhesion analyses showed that Gal-9 can bridge human circulating and naïve B cells to vascular endothelial cells (EC), while decelerating transendothelial migration. Moreover, Gal-9 interactions with naïve B cells induced global transcription of gene families related to regulation of cell signaling and membrane/cytoskeletal dynamics. Signaling lymphocytic activation molecule F7 (SLAMF7) was among key immunoregulators elevated by Gal-9-binding, while SLAMF7’s cytosolic adapter EAT-2, which is required for cell activation, was eliminated. Gal-9 also activated phosphorylation of pro-survival factor, ERK. Together, these data suggest that Gal-9 promotes B cell – EC interactions while delivering anergic signals to control B cell reactivity. Currently I am working on implementing the novel Gal-9/B cell interaction to target malignancies and autoimmune disorders.
Altered pancreatic cancer glycome and disease prognosis (Bellis lab)
My dissertation research identified addition of α2-6 linked sialic acid addition by sialyltransferase ST6Gal-I as a determinant of gemcitabine resistance in PDAC. ST6Gal-I was shown to hinder chemotherapy dependent DNA damage and lead to dysregulation of genes involved in gemcitabine metabolism. In the next part of my thesis I analyzed the role of ST6Gal-I in PDAC progression. I generated a novel mouse of PDAC by pancreases specific knock in of ST6Gal-I along with oncogenic K-Ras. Oncogenic K-Ras is the driving mutation of PDAC. ST6Gal-I knock in significantly reduced survival along with increased metastasis. Mechanistic investigation depicted crosstalk between increased sialylation with increase Sox9, key ductal marker, expression. Sox9, is a driver of acinar to ductal metaplasia, which is one of the earliest steps in disease progression. To study initiation we mimicked pancreatitis by caerulin treatment in our mouse model. ST6Gal-I knock in mice had significantly increased ADM compared to control. Single cell RNA sequencing depicted increased ductal as well as acinar gene expression in mice pancreas with increased ST6Gal-I expression. Interestingly Sox9, the ductal fate determinant gene was aberrant over expressed in acinar nuclei of ST6Gal-I knock in mice. These striking observations of ST6Gal-I dependent aggravation of PDAC progression depicted heavy dependence of PDAC on altered sialylation of surface receptors. This opens up a plethora of questions for further investigation. Together my work placed ST6Gal-I as a key player in PDAC initiation, pathogenesis and therapy resistance.