Abstract
BackgroundSeveral reports indicate a commonly deleted chromosomal region independent from, and distal to the TP53 locus in a variety of human tumors. In a previous study, we reported a similar finding in a rat tumor model for endometrial carcinoma (EC) and through developing a deletion map, narrowed the candidate region to 700 kb, harboring 19 genes. In the present work real-time qPCR analysis, Western blot, semi-quantitative qPCR, sequencing, promoter methylation analysis, and epigenetic gene expression restoration analyses (5-aza-2´-deoxycytidine and/or trichostatin A treatments) were used to analyze the 19 genes located within the candidate region in a panel of experimental tumors compared to control samples.ResultsReal-time qPCR analysis suggested Hic1 (hypermethylated in cancer 1), Inpp5k (inositol polyphosphate-5-phosphatase K; a.k.a. Skip, skeletal muscle and kidney enriched inositol phosphatase) and Myo1c (myosin 1c) as the best targets for the observed deletions. No mutation in coding sequences of these genes was detected, hence the observed low expression levels suggest a haploinsufficient mode of function for these potential tumor suppressor genes. Both Inpp5k and Myo1c were down regulated at mRNA and/or protein levels, which could be rescued in gene expression restoration assays. This could not be shown for Hic1.ConclusionInnp5k and Myo1c were identified as the best targets for the deletions in the region. INPP5K and MYO1C are located adjacent to each other within the reported independent region of tumor suppressor activity located at chromosome arm 17p distal to TP53 in human tumors. There is no earlier report on the potential tumor suppressor activity of INPP5K and MYO1C, however, overlapping roles in phosphoinositide (PI) 3-kinase/Akt signaling, known to be vital for the cell growth and survival, are reported for both. Moreover, there are reports on tumor suppressor activity of other members of the gene families that INPP5K and MYO1C belong to. Functional significance of these two candidate tumor suppressor genes in cancerogenesis pathways remains to be investigated.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0238-4) contains supplementary material, which is available to authorized users.
Highlights
Several reports indicate a commonly deleted chromosomal region independent from, and distal to the TP53 locus in a variety of human tumors
Real-time quantification PCR To determine potential target genes for the observed frequent allelic imbalance (AI)/deletions distal to the Tp53 gene [10], we determined the expression profile of all the 19 genes located in this region in a panel of 28 rat primary tumor and seven non-malignant endometrium (NME) cell cultures
The question was whether the observed reduced expression of these nine genes was due to the physical deletion of the genetic material or other regulatory mechanisms
Summary
Several reports indicate a commonly deleted chromosomal region independent from, and distal to the TP53 locus in a variety of human tumors. Subsequent analysis, revealed that Tp53 was not the only target [10], and the observed pattern for AI, chromosomal breaks and deletions suggested that major selection was directed against a region located close to, but distal of Tp53. This independent, commonly deleted chromosomal segment at RNO10q24-q25 is homologous to the frequently reported loci of tumor suppressor activity on 17p13.3 in several human malignancies [6,7,8,9]. Statistical analysis of qPCR results combined with subsequent gene mutation screening along with epigenetic and protein expression analyses suggested Inpp5k and Myo1c as the most prominent target tumor suppressor candidates in this region
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