The novel human MOST-1 (C8orf17) gene exhibits tissue specific expression, maps to chromosome 8q24.2, and is overexpressed/amplified in high grade cancers of the breast and prostate

Abstract

Aims: To elucidate genes that participate in the process of oncogenesis, primers based on the E6 genes of genital human papillomaviruses (HPVs) were used to amplify potential expressed sequence tags (ESTs) from the MOLT-4 T lymphoblastic leukaemia cell line.

Methods: Using the polymerase chain reaction (PCR) with human papillomavirus E6 gene primers, an EST from the MOLT-4 T lymphoblastic leukaemia cell line was amplified. Via rapid amplification of cDNA ends (RACE) and cycle sequencing from MOLT-4 and fetal lung cDNA libraries, overlapping cDNAs of 2786 bp and 2054 bp of the corresponding novel human intronless gene designated MOST-1 (for MOLT-4 sequence tag-1) were characterised and assigned the symbol C8orf17 by the HUGO Nomenclature Committee.

Results: Both cDNAs contained a potential open reading frame (ORF) of 297 bp incorporating a methionine codon with an ideal Kozak consensus sequence for translation initiation, and encoding a putative hydrophilic polypeptide of 99 amino acids. Although reverse transcription PCR (RT-PCR) demonstrated MOST-1 expression in all 19 cancer and two normal cell lines tested, differential expression was seen in only nine of 16 normal tissues tested (heart, kidney, liver, pancreas, small intestine, ovary, testis, prostate, and thymus). A 388 bp fragment was amplified from the NS-1 mouse myeloma cell line, the sequence of which was identical to that within the MOST-1 ORF. The MOST-1 gene was mapped by fluorescent in situ hybridisation to chromosome 8q24.2, a region amplified in many breast cancers and prostate cancers, which is also the candidate site of potential oncogene(s) other than c-myc located at 8q24.1. Analysis of paired biopsies of invasive ductal breast cancer and adjacent normal tissue by semiquantitative and real time RT-PCR revealed average tumour to normal ratios of MOST-1 expression that were two times greater in grade 3 cancers than in grade 1 and 2 cancers. Quantitative real time PCR of archival prostatic biopsies displayed MOST-1 DNA values that were 9.9, 7.5, 4.2, and 1.4 times higher in high grade carcinomas, intermediate grade carcinomas, low grade carcinomas, and benign hyperplasias, respectively, than in normal samples.

Conclusions: These data suggest a role for MOST-1 in cellular differentiation, proliferation, and carcinogenesis.

Figure 1

(A) cDNA sequence of the human MOST-1 gene (GenBank accession number AF220264). The 2786 nucleotide (nt) sequence was derived from the MOLT-4 cDNA library, whereas an overlapping and identical 2054 nt sequence (nt 664–2705) was generated from a human fetal lung cDNA library. The italicised nucleotides in bold face correspond to the 3′ segments of primers targeting human papillomavirus E6 genes. MOST-1 cDNA contains a potential open reading frame of 297 nt (nt 1115–1411), encoding 99 amino acids, with the presumed translation start and termination codons within boxes. Three potential mRNA destabilising signals (ATTTA) are shown as underlined nucleotides. (B) Deduced amino acid sequence of a putative MOST-1 polypeptide comprising 99 residues.

Figure 2

Chromosomal localisation of the MOST-1 gene. (A) Double fluorescence in situ hybridisation signals detected by a MOST-1 specific probe at chromosome region 8q24.2, indicated by the arrow. (B) DAPI staining of the same mitotic figure to identify chromosome 8.

Figure 3

Correlation between histological types of prostatic tissues with MOST-1 DNA values. NML and BPH refer to normal prostate and benign prostatic hyperplasia, respectively. LGC, IGC, and HGC denote increasing grades of prostatic cancer (low, intermediate, and high), corresponding to Gleason scores of 3–5, 6–7, and 8–9, respectively. MOST-1 DNA values were calculated according to the formula 2^-ΔC_T, where ΔC_T equals the difference between the threshold cycles for MOST-1 and G3PDH (glyceraldehyde-3-phosphate dehydrogenase) gene detection by real time polymerase chain reaction. The horizontal bars indicate mean values.