Abstract 4464: Biological functions of LSAMP, a gene frequently deleted in African American prostate cancers
Authors: Tan Shyh-Han , Babcock Kevin , Kohaar Indu , Mohamed Ahmed A. , Young Denise , Srivastava Shiv , Dobi Albert 
Published: July 2017

Introduction: Most genomic studies of prostate cancer (CaP) have been performed primarily on men of European ancestry, including Caucasian Americans. African Americans (AA) men, however, bear the burden of highest CaP incidence and mortality rates in the US. Cumulative data from other groups and from us have shown significantly lower rate of alterations of the two common CaP driver genes (PTEN and ERG) in AA CaP as compared to CA CaP. Using a combination of whole genome sequencing, IHC and FISH based validations on tissue microarrays, and analysis of the TCGA data from a total of 438 CaPs, we recently reported a higher frequency of a genomic deletion on 3q13.31 locus in AA CaP which also associated with rapid biochemical recurrence. This deletion is centered at the LSAMP (Limbic System Associated Membrane Protein) gene. The LSAMP protein functions as a cell adhesion molecule affecting cell differentiation and migration during development. We hypothesize that the loss of LSAMP contributes to CaP progression. Here, we report the biological consequence of LSAMP modulation in CaP cells.

Methods: LSAMP status in CaP cell lines (LNCaP, MDAPCa2b, CWR22rv1, LAPC4, NCI-H660, and PC3) was assessed by FISH, immunoblot, qRT-PCR and immuno-fluorescence (IF), assays using MC-IXC neuroepithelioma cell line as the positive control. We established doxycycline inducible LSAMP in LNCaP and in MDAPCa2b (an AA patient derived cell line with monoallelic LSAMP deletion) cells, and constitutive expression in DU145 cells. The effect of LSAMP loss and over-expression on cell growth, proliferation apoptosis and cell migration was monitored by MTT, soft-agar, and Boyden chamber assays.

Results: Of the CaP cell lines analyzed, LSAMP RNA and protein expression was detected in PC3 and NCI-H660. IF assay showed that endogenously expressed LSAMP is predominanty localized to the cell surface. Exogenous expression of LSAMP, either constitutively in DU145, or by inducible means in LNCaP and MDAPCa2b cells, showed similar localization to the plasma membrane. Both inducible and constitutive overexpression of LSAMP resulted in reduced cell growth. LSAMP expression in DU145 resulted in enhanced formation of filamentous extracellular extensions. Analysis of published TCGA (The Cancer Genome Atlas) data showed a correlation of high LSAMP promoter methylation and low LSAMP expression in CaP tumors compared to normal prostate tissues.

Conclusion: The cell biology features of LSAMP reported here, together with observations of genomic deletion and methylation of LSAMP promoter in CaP, support its role in CaP development or progression. These data support the function of LSAMP as a tumor suppressor gene, as previously reported in other cancers.

Citation Format: Shyh-Han Tan, Kevin Babcock, Indu Kohaar, Ahmed A. Mohamed, Denise Young, Shiv Srivastava, Albert Dobi. Biological functions of LSAMP, a gene frequently deleted in African American prostate cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4464. doi:10.1158/1538-7445.AM2017-4464