Hypermethylation, but not LOH, is associated with the low expression of MT1G and CRABP1 in papillary thyroid carcinoma

Abstract

We previously obtained gene expression profiles of 8 matched papillary thyroid carcinoma (PTC) and normal tissues using DNA microarrays. To identify novel tumor suppressor genes involved in thyroid carcinogenesis, we here analyze genes showing lower expression in PTC tumors than in normal thyroid tissues. A search for loss of heterozygosity (LOH) in 49 regions that harbor consistently down-regulated genes revealed LOH in only 4 regions and in just a very small number of tumors. To determine whether the underexpression might be due to promoter methylation, we used combined bisulfite restriction analysis and bisulfite sequencing to study 7 underexpressed genes. Loss of expression of MT1G and CRABP1 is accompanied by hypermethylation in the 5 regions of these genes, but methylation was not seen in other genes tested. Combined treatment with the DNA methyltransferase inhibitor 5-aza-2-deoxycytidine (5-Aza-dC) and the histone deacetylase inhibitor trichostatin A (TSA) resulted in demethylation and re-expression of the MT1G gene in the cell line K2. Treatment with 5-Aza-dC alone restored CRABP1 expression in a colorectal cancer cell line, SW48. In conclusion, LOH is a remarkably rare mechanism of loss of gene function in PTC. In contrast, hypermethylation of promoter CpG islands seems to occur at higher frequency. MT1G and CRABP1 are novel genes that are likely involved in the pathogenesis of sporadic PTC.

Aberrant Expression of Retinoic Acid Signaling Molecules Influences Patient Survival in Astrocytic Gliomas

“…In the present study, we investigated potential alterations in the RA pathway and analyzed their clinical relevance. In contrast to findings in other tumor entities, [7][8][9][10][11][12][13][14] we observed a marked up-regulation of key molecules associated with increased RA availability and alternative, prosurvival RA usage in gliomas. This was accompanied by increased intratumoral levels of RA precursors and activated RA.…”

“…Notably, CRABP1, which channels RA to endosomal compartments, passing it on to degradation by CYP26 enzymes, 12 showed increased expression levels in tumor biopsy samples, compared with nontumorous brain ( Figure 3A), although expression of CRABP1 was similarly distributed among different WHO grades ( ϭ 0.02, P ϭ 0.81; Figure 3C; see also Supplemental Figure S4A at http://ajp.amjpathol.org) and was not associated with patient survival ( Figure 3E). Whether CRABP1 in astrocytic gliomas can participate in the degradation of RA depends on the availability of catabolic CYP26 enzymes.…”

“…4 -6 Various types of human cancers show abnormalities in the RA signaling pathway. [7][8][9][10][11][12][13][14] In particular, epithelial tumors, which originate from tissues that depend on a closely orchestrated balance between cellular proliferation and subsequent differentiation, show loss of RA signaling components involved in RA availability. This frequently includes altered expression of cellular retinolbinding protein 1 (CRBP1), an intracellular transport protein in charge of facilitating the uptake of RA precursor molecules, [7][8][9] and of aldehyde dehydrogenase 1A1 (ALDH1A1), which is capable of activating RA precursors into the active RA metabolite, 10,11 as well as of cellular retinoic acid binding protein 2 (CRABP2) and cellular retinoic acid binding protein 1 (CRABP1), two chaperone proteins that shuttle between different cellular compartments channeling RA to designated nuclear RA receptors or to endosomal degradation by cytochrome P450, family 26 members (CYP26), respectively.…”

“…This frequently includes altered expression of cellular retinolbinding protein 1 (CRBP1), an intracellular transport protein in charge of facilitating the uptake of RA precursor molecules, [7][8][9] and of aldehyde dehydrogenase 1A1 (ALDH1A1), which is capable of activating RA precursors into the active RA metabolite, 10,11 as well as of cellular retinoic acid binding protein 2 (CRABP2) and cellular retinoic acid binding protein 1 (CRABP1), two chaperone proteins that shuttle between different cellular compartments channeling RA to designated nuclear RA receptors or to endosomal degradation by cytochrome P450, family 26 members (CYP26), respectively. [12][13][14] In addition, recent studies on breast tumor cells revealed a pathological involvement of the intracellular transport protein fatty acid binding protein 5 (FABP5) in neoplastic RA signaling. 15,16 FABP5 was shown to inhibit RA-induced differentiation and induce survival/proliferation of tumor cells after diverting RA to an alternative pathway.…”

DNA methylation profile of 28 potential marker loci in malignant mesothelioma

“…Epigenetic regulation has been implicated in the control of various MT genes [49]. Hypermethylation of the MT1G promoter has been reported to be associated with higher tumor stage in prostate cancer [50], and MT3 and MT1G expression are downregulated by methylation in oesophageal cancer and thyroid carcinoma respectively [51,52]. The biological role of silencing of these metal-binding proteins in cancer remains to be further investigated.…”