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TRANSMEMBRANE PROTEIN 97; TMEM97

TRANSMEMBRANE PROTEIN 97; TMEM97

Alternative titles; symbolsMAC30HGNC Approved Gene Symbol: TMEM97Cytogenetic location: 17q11.2 Genomic coordinates (GRCh38): 17:28,319,040-28,328,684 (from N...

Alternative titles; symbols

  • MAC30

HGNC Approved Gene Symbol: TMEM97

Cytogenetic location: 17q11.2 Genomic coordinates (GRCh38): 17:28,319,040-28,328,684 (from NCBI)

▼ Description
TMEM97 is a conserved integral membrane protein that plays a role in controlling cellular cholesterol levels (Bartz et al., 2009).

▼ Cloning and Expression
Using a phage subtraction library to identify genes expressed in normal leptomeningeal cells but not in a meningioma cell line, followed by RT-PCR, Murphy et al. (1993) cloned TMEM97, which they called MAC30. Northern blot analysis detected transcripts of about 2.3 and 2.8 kb in normal leptomeningeal cells and in a cell line derived from these cells.

Using differential display RT-PCR to identify genes expressed in fetal but not adult liver, Malhotra et al. (1999) obtained a partial MAC30 clone. Northern blot analysis detected transcripts of about 2.3 and 2.8 kb in 10-, 16-, and 20-week fetal liver, but not in adult liver.

Using real-time quantitative PCR, Kayed et al. (2004) found variable MAC30 expression in all normal human tissues examined, with highest expression in testis and stomach and lowest expression in thyroid, thymus, and adipose tissue. In situ hybridization detected MAC30 in normal pancreatic acini, islets, and large ducts. Immunohistochemical analysis showed MAC30 protein in the cytoplasm of peripheral pancreatic islet cells, in endothelial and smooth muscle cells of blood vessels, and in nerves, monocytes, and fibroblasts. In esophagus, MAC30 was detected in cytoplasm of mucosal cells, particularly in the superficial and intermediate epithelial layers. Gastric submucosa and muscularis and normal colonic epithelium exhibited staining patterns similar to that of esophagus.

Bartz et al. (2009) reported that the full-length 176-amino acid TMEM97 protein contains an N-terminal signal peptide and 4 transmembrane domains.

▼ Gene Function
Murphy et al. (1993) found that MAC30 expression was downregulated in meningiomas and Schwann cell tumors compared with normal leptomeningeal cells.

Kayed et al. (2004) found that expression of MAC30 was significantly increased in breast and colon cancers and significantly decreased in pancreatic and renal cancers compared with normal tissue.

Using microarray analysis, Wilcox et al. (2007) found that TMEM97 and several genes regulating cholesterol and lipid homeostasis were upregulated in cultured ovarian surface epithelial (OSE) cells treated with progesterone. TMEM97 was the most highly upregulated gene identified. Real-time quantitative RT-PCR analysis showed that TMEM97 expression was downregulated in ovarian cancer cells relative to normal OSE cells. Database analysis suggested that expression of TMEM97 is coregulated with that of cholesterol biosynthesis genes in normal human tissues. Wilcox et al. (2007) proposed that TMEM97 may play a role in cholesterol and lipid metabolism.

Using genomewide expression profiling and RT-PCR, Bartz et al. (2009) found that TMEM97 was upregulated to an extent similar to that of LDL receptor (LDLR; 606945) following sterol depletion in HeLa cells. TMEM97 expression was also upregulated following knockdown of LDLR via small interfering RNA (siRNA). Bartz et al. (2009) identified a sterol regulatory element-1 (SRE1) consensus sequence upstream of the TMEM97 transcription initiation site, and siRNA-mediated knockdown of SREBP2 (SREBF2; 600481) suppressed TMEM97 expression in sterol-depleted cells. Knockdown of TMEM97 via siRNA reduced the number of LDL-containing endosomes in HeLa cells and reduced cellular uptake of radiolabeled cholesterol. Restoration of TMEM97 expression rescued cellular cholesterol levels in TMEM97-knockdown cells. Fluorescence-tagged TMEM97 localized to the endoplasmic reticulum in control HeLa cells, but it redistributed to perinuclear and plasma membrane lysosomal vesicles in sterol-depleted cells. TMEM97 coimmunoprecipitated with NPC1 (607623), a cholesterol-binding protein essential for efficient lysosomal cholesterol export. Interaction between TMEM97 and NPC1 was inversely proportional to cellular sterol content. Bartz et al. (2009) concluded that TMEM97 is an SREBP target gene that localizes to lysosomes under sterol depletion, directly or indirectly binds NPC1, and contributes to the regulation of cellular cholesterol levels.

▼ Mapping
Using a rodent/human somatic cell hybrid panel and a somatic cell hybrid containing a t(11;17) translocation, Murphy et al. (1993) mapped the TMEM97 gene to chromosome 17q21-qter. Kayed et al. (2004) stated that the TMEM97 gene maps to chromosome 17q11.2.

Tags: 17q11.2