Mechanistic and structural insights into a new pro-metastatic collagen glucosyltransferase - Lung cancer is the primary cause of cancer death in western countries, including the United States. Kentucky leads the nation both in lung cancer incidence and mortality. Lung cancer-related mortality is mainly due to metastasis. During metastasis, malignant tumors accumulate collagen fibrils to drive cancer cell dissemination and impede the influx of anti-tumor immune cells. The long-term goal of our laboratory is to determine the roles of collagen and collagen-modifying enzymes in metastasis to inform new therapeutic development. Toward that goal, we found that the collagen lysyl hydroxylase 2’s long alternatively spliced isoform b (LH2b), carrying an extra motif encoded by exon 13a, is a previously undetected collagen glucosyltransferase (GGT). GGT plays a major role in LH2’s pro-metastatic activity. High expression levels of LH2b predict a worse prognosis, while the expression levels of LH2’s short alternatively spliced isoform a (LH2a) without exon 13a are not prognostic. These findings provide a novel basis for the observation made by our group and many others that high LH2 expression has poor-prognostic value and drives the growth and metastasis of multiple cancer types, including lung cancer, breast cancer, and sarcoma. Thus, LH2 GGT is a new therapeutic target of interest. However, how LH2 GGT drives cancer metastasis is unclear and LH2 GGT inhibitor is not available, deficiencies that can be addressed only by gaining mechanistic insight into the structure-function of LH2 GGT. To elucidate how LH2 GGT enzymatic activity is structurally regulated, we solved 3 collagen GGT structures, including LH2 GGT and its mimiviral homolog. Our results suggested that LH2b forms a dimer with a continuous collagen-binding site and binds UDP-glucose cooperatively. Based on these findings, we hypothesized that LH2b’s unique structural features allow it to modify tumor stroma and drive metastasis. By testing this hypothesis, we will gain insights into 1) to what extent LH2b overexpression and LH2b-mediated collagen glucosylation happen in human lung cancer; 2) why LH2b drives tumor progression; 3) how LH2b GGT function is regulated; 4) what are LH2b GGT’s pro-metastatic structural features. The findings from this work will advance the understanding of the relevance and mechanism of LH2b in tumor progression and identify the structural features of LH2b GGT that drive cancer progression. Such insights will inform LH2b GGT cancer biology and inhibitor development.
