Transcription Regulation and Protein Subcellular Localization of the Truncated Basic Hair Keratin hHb1-ΔN in Human Breast Cancer Cells

Abstract

An aberrant truncated hHb1 hair keratin transcript, named hHb1-⌬N, was previously identified in breast carcinomas. No normal tissue tested so far, including hairy skin, expressed hHb1-⌬N, indicating that hHb1-⌬N is related to carcinogenesis. In the present study, we investigated the mechanism by which such truncated transcript was generated in breast cancer cell lines. We found that hHb1-⌬N transcription is initiated at an unusual cryptic promoter within the fourth intron of the hHb1 gene and is dependent on two proximal Sp1 binding sites for its baseline activity. Moreover, hHb1-⌬N transcription is increased in response to DNA demethylation by the 5-aza-2-deoxycytidine drug. This induction is dependent on protein neosynthesis, indicating that an additional factor is required. In addition, we showed that the hHb1-⌬N transcript is translated in vivo as a truncated hHb1 protein that is missing the 270 amino-terminal residues. The hHb1-⌬N protein exhibits a filament pattern throughout the cytoplasm and partially co-localizes with cytokeratin filaments, indicating its participation in the cytoskeleton network. hHb1-⌬N might alter the adhesive properties of cancer cells.

Upregulation of the truncated basic hair keratin 1(hHb1‐ΔN) in carcinoma cells by Epstein‐Barr virus (EBV)

“…Alternatively, the inhibition of methylation is indirect and mediated by a cis‐acting factor. hHb1‐ΔN promoter contains an Sp1 binding site 28. However, we found no significant difference in Sp1 expression by RT‐PCR between EBV‐positive, ‐negative and 5‐Aza‐CdR‐treated cells (data not shown).…”

“…Boulay et al had detected green fluorescence protein (GFP)‐fused hHb1‐ΔN protein associated with a filamentous network in the cytoplasm of transfected Hela cells 28. In EBV‐positive NU‐GC‐3 cells, we detected fibrous structures in the cytoplasm that resemble the keratin network.…”

“…These data are consistent with the possibility that EBV upregulates hHb1‐ΔN expression through a decrease in CpG methylation. hHb1‐ΔN was shown to be a product of alternative initiation of transcription from a site located in the intron 4 of the hHb1 gene 28. Intron 4 does not contain CpG residues, whereas there are several CpG sites at the end of exon 4 and at the beginning of exon 5.…”

In silico Analysis of Combinatorial microRNA Activity Reveals Target Genes and Pathways Associated with Breast Cancer Metastasis

“…Over-expression of the truncated form was also reported in four Epstein-Barr virus infected epithelial carcinoma cell lines 91. Using several breast cancer cell lines, it was determined that the truncated form of the gene was transcribed through an alternative promoter located in the fourth intron of the gene 92. The authors demonstrated that the protein product of hHb1-ΔN participates in cytoskeleton structure, and they suggested that it may alter the adhesive properties of cancer cells.…”

The oncogenic potential of a prostate cancer‐derived androgen receptor mutant

“…In addition, some of upregulated genes that are involved in various cellular functions may also contribute to AR K580R -caused tumorigenesis. These include SPOCK2 (TESTICAN 2) which promotes the migration of tumor cells by abolishing inactivation of membrane-type matrix metalloproteinases (MT-MMPs) [26], KRTHB1 (keratin, hair, basic, 1) which is associated with carcinogenesis in breast tissue [27], IL27RA (interleukin 27 receptor, alpha) which is essential for transcriptional activation of STAT1 [28], NEK6 (never in mitosis gene a-related kinase 6) that is an activator of the NF-kappaB and MAPK signaling pathways [29], and ZNF7 (zincfinger gene-7) that has a role in the MAPK signaling pathway [30]. Among the 10 downregulated genes in the AR K580R pRNS-1-1 subline, silencing of MECP2 (methyl CpG binding protein 2) expression is known to be common in human CaP [31].…”