SLIDES & TRANSCRIPTS
Saturday, December 6, 2003

The Genetics and Biology of MSR1

Jianfeng Xu, M.D.

I think first I will give you an overview of the current status of the susceptibility gene, so you can find MSR in this whole picture. In this area, we can summarize three things. Number one, during the last ten years we have made great progress in finding the prostate cancer susceptibility gene. There are several large scale hereditary or familial prostate cancer family has been established. We have an NCI funded institution consortium which combines over 15 groups worldwide to address this issue, which assembled over 1500 hereditary prostate cancer family, which give us significant improved power to identify prostate cancer gene, considering this heterogeneous issue is much needed.

On the other hand, if you compare to other major cancers, this area is very behind. Unlike breast cancer and colon cancer so far, there is no clear-cut major prostate cancer susceptibility gene so far. But setting this aside, we still make good progress, especially during the last two years. There are five genes that have been proposed as a major susceptibility gene.

The number one is HPC2 on chromosome 17, which has been identified in a Utah family. The number two is iron cell identified in Hopkins family collection by a collaborative group in Hopkins , Cleveland Clinic and Wake Forest . The one that I am going to talk about, the MSR1 gene, is also identified from Johns Hopkins' family collection, which was identified by Johns Hopkins and the Wake Forest group. The next two gene is not typically identified through this hereditary form, but is identified through a candidate gene approach.

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This is the general approach that we used for the last ten years to identify those prostate cancer susceptibility genes. The first is obvious. You have to collect a family, and then you perform linkages. There is this identified region likely to contain those major gene, and then you select the gene in that region and sequence those genes in a program, after you identify mutation and you ask whether those mutation actually segregate with prostate cancer, and test those mutation in a larger population. That is exactly what we did with a gene on chromosome 8p.

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The reason we studied chromosome 8p for the last three years is the following. The number one of course is evidence from linkage analysis, in which several groups, including ours showed there is a linkage bridging on chromosome 8p. Number two, obvious, you all well know that 8p is most allele-bridging in prostate cancer. Lastly, we know 8p has a germ line emerging which is very frequent. About 26 percent of Caucasians have this five MET base emerging.

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This just summarizes the linkage with 8p. This is the whole linkage curve 8p 223, you can see this region.

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This is an LH study, summarizes most of our previous studies, and you can see this 8p is the highest one.

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This again showing the inversion of 8p. We performed a linkage analysis and you can see this multiple recombinant here. The reason those are not really multiple recombinant but emerging, so if you use emerging, you can see this only single recombinant. This has been confirmed in the cytogenetic world.

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After we focus on this evidence, we narrow this small region which likely contains a prostate cancer susceptibility gene. You cannot see those, but the idea is , there are multiple genes in this region.

What we did the last three years is systematically evaluate each of those genes, using a high throughput sequencing and the genotyping approach, which is one by one systematic.

TOP

One of those genes is the MSR1 gene, which is a multifunctional gene. This gene also is called scavenger receptor type A, so SRA. The genomic size is about 90 KB, with a eleven axons, three isoform; two are functional, one is non-functional, and expressed exclusively in inflammatory cells, especially macrophage. It binds with diverse ligand, especially the LDL, modified LDL.

These are SRA1 knockout mice. These knockout mice show two things. One is less susceptible to form cell formation, so it is decreased atherosclerosis. The other thing which is probably relevant to us is, more susceptible to certain pathogens.

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This is a cartoon showing multiple function of this macrophage scavenger. This MSR1 is really necessary for macrophage and host cell interaction. It is critical -- that is actually one of the major functions is adhesion, so it is involved in the recruitment and the retention of macrophage in the region. So this is a critical function for macrophage, and also that is where endocytosis and phagocytosis, especially to the bacteria and virus, and the clearance of and detoxification of those products. So it does have multiple function, and it is not clear which function is potentially related to the cancer development. But we hypothesize maybe it is involved in adapt immunity which is linked to the cancer development.

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So we choose one gene, and we sequenced this gene, the intron and exon and promoter region, and what we found, we found several key mutations.

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After we identify the mutations, we want to see whether those mutations actually segregate with prostate cancer.

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So we do linkage, we do the co-segregation, and do a series analysis on that,

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and due to time limitation, I am just showing one pedigree. All those solid squares are affected with prostate cancer, and the solid dot are the mutation carrier and open dot here are non-carrier. So what you can see is a complete segregation of this chunk of mutations with prostate cancer.

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Similarly you can see this co-segregation in the family.

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This is showing one of the chunks of mutations in prostate cancer family in sporadic cases in population control and effect control. You can see a decrease.

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And similar with another mutation, which is a functionally important(?) mutation. This mutation is associated with clinical significance of prostate cancer.

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At this stage, I have to say the replication of this MSR1 gene is very controversial. There are several positive findings and several negative findings to reject the MSR1 gene. I think we can summarize into two things. This gene appear to be very well replicated in African-American populations. In Caucasians however it is controversial.

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We performed a functional study, not only see this mutation is high in cancer, we also see the expression of this mutation. So this is a normal patient with a normal expression of MSR1 gene, and this is a colon(?) carrier, and this is no expression. We are using CD68 to show the macrophage.

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