t(2;8)(q32;q12.1)

COL3A1 (collagen type III alpha 1 chain)

2q32.2

Mutations in this gene are associated with Ehlers-Danlos syndrome types IV, and with aortic and arterial aneurysms. (Lee et al., 2008; Jeong et al., 2012)

The COL3A1 gene, located at chromosome 2q32, contains 51 exons spanning 38.43 kb of genomic distance. Two transcripts, resulting from the use of alternative polyadenylation sites, have been identified for this gene (GeneCards GCID:GC02P189803 (http://www.genecards.org/cgi-bin/carddisp.pl?gene=COL3A1), UniProt P02461-CO3A1_HUMAN (http://www.uniprot.org/uniprot/P02461)).

The gene encodes a protein of 1466 amino acids (aa) (138kDa). The shorter isoform is missing 847-1149 aa. The protein is the pro-alpha1 chains of type III collagen, a fibrillar collagen that is found in extensible connective tissues such as skin, lung, uterus, intestine and the vascular system, and is frequently found in association with type I collagen. The C-terminal propeptide, also known as the COLFI domain, has crucial roles in tissue growth and repair, in which it controls both the intracellular assembly of procollagen molecules and the extracellular assembly of collagen fibrils. It binds a calcium ion which is essential for its function (GeneCards GCID:GC02P189803(http://www.genecards.org/cgi-bin/carddisp.pl?gene=COL3A1), UniProt P02461-CO3A1_HUMAN (http://www.uniprot.org/uniprot/P02461)).

PLAG1 (Pleomorphic adenoma gene 1)

8q12.1

The gene spans about 50 kb and includes 5 exons. The size of the transcript is about 7 kb. It has two alternative splicing forms (one without exon 2) (GeneCards GCID:GC08M057073 (http://www.genecards.org/cgi-bin/carddisp.pl?gene=PLAG1), UniProt Q6DJT9-PLAG1_HUMAN (http://www.uniprot.org/uniprot/Q6DJT9)).

The gene encodes a 500-aa zinc finger protein (74 kDa) with two putative nuclear localization signals (Kas et al., 1997). When activated, it acts as a transcription factor that up-regulates target genes, such as IGFII, leading to uncontrolled cell proliferation. When overexpressed in cultured cells, it increases the proliferation rate and transformation. Other target genes such as CRLF1, CRABP2, CRIP2, PIGF are strongly induced in cells with PLAG1 induction. PLAG1 is a proto-oncogene whose ectopic expression can trigger the development of lipoblastomas and pleomorphic adenomas of the salivary gland (Hensen et al., 2002; Voz et al., 2004; Zatkova et al., 2004) (GeneCards GCID:GC08M057073 (http://www.genecards.org/cgi-bin/carddisp.pl?gene=PLAG1), UniProt Q6DJT9-PLAG1_HUMAN (http://www.uniprot.org/uniprot/Q6DJT9)).

The fusion occurs as a result of a cryptic, intrachromosomal rearrangement in tumors with apparently normal karyotypes. Comparison of the fusion gene with the wild type reveals that the fusion gene is associated with the t(2;8)(q31;q12.1) translocation. The first exon of COL3A1 is fused to either exon 2 or exon 3 of PLAG1 (Yoshida et al., 2014).

PLAG1 has a genomic fusion breakpoint in intron 1 resulting in alternative splicing of exon 2. The start codon of PLAG1 is located in exon 4 (Van Dyck et al., 2007), and the coding sequence of PLAG1 is preserved (Yoshida et al., 2014). This supports the molecular mechanism of overexpression of PLAG1 through promoter swapping: as a result of the translocation, the constitutively active promoter of the partner gene drives the ectopic expression of PLAG1 (Hibbard et al., 2000)

RT-PCR using total RNA extracted from frozen tumor tissue. The COL3A1/PLAG1 fusion transcript was amplified with primers 5-AGGGGAGCTGGCTACCCTCC-3 (forward), and, 5-ACGTTTCCCTGAAGGGACTT-3 (reverse). COL3A1/PLAG1-fusion transcripts of 345 bp and 450 bp were detected (Yoshida et al., 2014).

No fusion protein exist for reasons the above.

PLAG1 protein localizes to the nucleus (Bahrami et al.,2012).