Joseph Blake: SNP rs1143678 and B cell biology in SLE

Joseph Blake

Poster presenter: Joseph Blake, graduate student, University of Alabama, Birmingham

Poster title: An SLE-linked ITGAM Gene Variant Changes Mac-1 Structure, Signaling, and Surface Expression and Enhances IFNg Production and Antigen Presentation by B Cells

Scheduled poster session day and time: Friday, Nov. 6, 9 – 11 a.m. EST

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What is your poster about?

We found that the systemic lupus erythematosus (SLE)-associated SNP rs1143678 might affect the structure and function of the associated protein CD11b and looked into how this might impact B cell biology and, ultimately, SLE. Rs1143678 encodes the CD11b amino acid substitution Pro1146Ser. This is interesting because it provides a phosphorylation site four amino acids downstream from the canonical CD11b phosphorylation site at 1142Ser that is known to control Mac-1 activation. In B cells we have the first evidence that both serines appear to be constitutively phosphorylated, and that this changes the cells’ signaling equilibrium. Specifically, by proteomics analysis we inferred that B cells that are homozygous for the SNP over-express proteins associated with response to INF-γ, with antigen processing and presentation, and with the formation of focal adhesions. 

Why did you decide to investigate this topic?

I’m a soon-to-graduate student in the laboratory of senior author Alexander J. Szalai, PhD. Dr. Szalai and his group began to pursue this project based on the results of genome-wide-association studies published around 2008 that identified that a series of single nucleotide polymorphisms (SNPs) in the Integrin Alpha M (ITGAM) gene are associated with systemic lupus erythematosus (SLE). One of my mentors on this project, Dan Bullard, PhD, is an expert on ITGAM biology, and he, Jeff Edberg, PhD, and Dr. Szalai combined their skills and ideas to pursue this question. Integrin Alpha M encodes the protein CD11b, which pairs with CD18 to form the heterodimeric receptor called Mac-1. This integrin is primarily studied on myeloid cells, and its expression is reportedly approximately tenfold higher than on B cells. But it’s B cells that produce the autoantibodies associated with SLE. Preliminary experiments we did using Epstein Barr Virus-transformed B cells (from donors homozygous for the SLE-associated SNP) led to the initial observations that led to my project.

What excites you most about your work?

I’m most excited about how the project has expanded as we get more data. What started as a methodical measurement of protein structure and function has exploded into something that may affect our understanding of SLE pathogenesis.

What are you working on next related to this poster? 

Although the story has not yet completely unfolded (thus the abstract), we can say with confidence that the data we have so far supports our claims; of course, we still need to expand on these data for publication of our manuscript.