The first member of the human MAGE family was identified as a gene encoding a tumor-specific antigen in melanoma cells. Since then, the MAGE gene family has extensively increased in complexity with the conservation of the typical signature domain (Mage Homology Domain; MHD). The MAGE family has been divided in two big subfamilies: type-I and type-II MAGE family. Type-I MAGE family includes MAGE-A, B, and C, which are located as clusters on the X chromosome. They are completely silent in normal tissues, with the exception of male germ cells and placenta. Some of them are expressed in tumor cells of various histological types, where they code for antigens recognized by cytolytic T lymphocytes (CTL) in a major histocompatibility complex (MHC)-restricted way. Type-II MAGE family includes genes which encode different proteins containing MHD with undefined chromosome clustering. These genes differ from the type-I MAGE family by their genomic structure: they do not encode the antigenic peptide encoded by type-I MAGE and therefore will not trigger an immune response. This characteristic also gives them a different expression pattern compared to type-I MAGE: they are expressed in all normal tissues.
Figure 1-Family of human MAGE genes
Figure 2-RT-PCR of six NB cell lines; (A), RT-PCR of MAGE-A2; (B), RT-PCR of MAGE-A3; (C), RT-PCR of MAGE-A12; (D), RT-PCR of MAGE-D4; (E), RT-PCR of GAPDH; C=negative control; Lanes: IMR-32; SH-SY5Y; BE(2)-C; CB-JMN; LA1-5S; and SH-EP1. MAGE-A2, -A3, A12 do not expressed in IMR-32 and BE(2)-C cells, and MAGE-D4 expressed in all six cell lines.
Figure 3-Chromosomal location of MAGE-A2, -A3, -A12, MAGE-D4. The differences of expression pattern between MAGE-A and MAGE-D genes may due to their different location. So I further exam the expression of CSAG1 gene, which is not related to MAGE family, but is located proximate to MAGE-A genes
Figure 4-RT-PCR of CSAG1 in six NB cell lines; C=negative control; Lanes: IMR-32; SH-SY5Y; BE(2)-C; CB-JMN; LA1-5S; and SH-EP1; CSAG1 also do not expressed in IMR-32 and BE(2)-C cells, which is similar to the result from MAGE-A2, -A3, and A12.
The differential expression patterns of MAGE A2, A3, and A12 among the 6 different cell lines are very similar to each other, but D4 is expressed in all 6 cell lines.
CSAG1 is located at Xq28, is proximate to the MAGE-A genes.Expression of the CSAG1 gene in the 6 different cell lines is similar to that of MAGE A2, A3, and A12.
I would like to thank Dr. Rubin for his guidance and advices. Also thank Leleesha Samarawera and Bo Liu for their continuous help and patience. Additional thanks to Dr. Robert Ross for providing me with the cell lines.
|This document was last modified 05/12/2009.|
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