Robin Antrobus

Ovarian cancer is the fourth most common cancer in women in the Western world. In a pilot scale study, we highlight changes in the total serum glycome of patients with advanced ovarian cancer that might shed insight into disease pathogenesis. These changes include increases in levels of core fucosylated, agalactosyl biantennary glycans (FA2) and sialyl Lewis x (SLe(x)). To investigate further which proteins contribute to these alterations, we developed technology to analyze simultaneously the glycosylation of protein glycoforms contained in single spots excised from a 2D gel (<1 ng protein). The acute-phase proteins, haptoglobin, alpha1-acid glycoprotein, and alpha1-antichymotrypsin from patients contained elevated levels of subsets of glycoforms containing SLe(x). We also established that IgG heavy chains from patients contained twice the level of FA2 compared with healthy controls. Serum CA125 is the only biomarker that is used routinely, and there is a need for complementary markers that will improve both sensitivity and specificity. There was some preliminary indication that combinations of changes in the serum glycome might improve the separation of ovarian cancer and benign tumors; however, a larger study using data receiver operating characteristic curves will be required to draw any firm conclusions.

Forward genetic screens in Drosophila melanogaster for modifiers of position-effect variegation have revealed the basis of much of our understanding of heterochromatin. We took an analogous approach to identify genes required for epigenetic repression in human cells. A nonlethal forward genetic screen in near-haploid KBM7 cells identified the HUSH (human silencing hub) complex, comprising three poorly characterized proteins, TASOR, MPP8, and periphilin; this complex is absent from Drosophila but is conserved from fish to humans. Loss of HUSH components resulted in decreased H3K9me3 both at endogenous genomic loci and at retroviruses integrated into heterochromatin. Our results suggest that the HUSH complex is recruited to genomic loci rich in H3K9me3, where subsequent recruitment of the methyltransferase SETDB1 is required for further H3K9me3 deposition to maintain transcriptional silencing.

The retromer complex is required for the efficient endosome-to-Golgi retrieval of the CIMPR, sortilin, SORL1, wntless and other physiologically important membrane proteins. Retromer comprises two protein complexes that act together in endosome-to-Golgi retrieval; the cargo-selective complex is a trimer of VPS35, VPS29 and VPS26 that sorts cargo into tubules for retrieval to the Golgi. Tubules are produced by the oligomerization of sorting nexin dimers. Here, we report the identification of five endosomally-localised proteins that modulate tubule formation and are recruited to the membrane via interactions with the cargo-selective retromer complex. One of the retromer-interacting proteins, strumpellin, is mutated in hereditary spastic paraplegia, a progressive length-dependent axonopathy. Here, we show that strumpellin regulates endosomal tubules as part of a protein complex with three other proteins that include WASH1, an actin-nucleating promoting factor. Therefore, in addition to a direct role in endosome-to-Golgi retrieval, the cargo-selective retromer complex also acts as a platform for recruiting physiologically important proteins to endosomal membranes that regulate membrane tubule dynamics.

Aberrant glycosylation on glycoproteins that are either presented on the surface or secreted by cancer cells is a potential source of disease biomarkers and provides insights into disease pathogenesis. N-Glycans of the total serum glycoproteins from advanced breast cancer patients and healthy individuals were sequenced by HPLC with fluorescence detection coupled with exoglycosidase digestions and mass spectrometry. We observed a significant increase in a trisialylated triantennary glycan containing alpha1,3-linked fucose which forms part of the sialyl Lewis x epitope. Following digestion of the total glycan pool with a combination of sialidase and beta-galactosidase, we segregated and quantified a digestion product, a monogalactosylated triantennary structure containing alpha1,3-linked fucose. We compared breast cancer patients and controls and detected a 2-fold increase in this glycan marker in patients. In 10 patients monitored longitudinally, we showed a positive correlation between this glycan marker and disease progression and also demonstrated its potential as a better indicator of metastasis compared to the currently used biomarkers, CA 15-3 and carcinoembryonic antigen (CEA). A pilot glycoproteomic study of advanced breast cancer serum highlighted acute-phase proteins alpha1-acid glycoprotein, alpha1-antichymotrypsin, and haptoglobin beta-chain as contributors to the increase in the glycan marker which, when quantified from each of these proteins, marked the onset of metastasis in advance of the CA 15-3 marker. These preliminary findings suggest that specific glycans and glycoforms of proteins may be candidates for improved markers in the monitoring of breast cancer progression.