Human growth and transformation-dependent protein (HGTD-P), also called E2-induced gene 5 protein (E2IG5), is a
protein that in humans is encoded by the FAM162Agene on chromosome 3.[5][6] This protein promotes intrinsic
apoptosis in response to
hypoxia via interactions with hypoxia-inducible factor-1α (
HIF-1α).[5][7][8][9][10][11] As a result, it has been associated with cerebral
ischemia,
myocardial infarction, and various
cancers.[8][12][13]
Structure
HGTD-P contains two transmembrane domains that are required for its localization to the mitochondria and induction of cell death.[8]
Function
HGTD-P localizes to the mitochondria, where it participates in regulation of apoptosis.[5][8] This localization is aided by the chaperone
Hsp90, which is required to stabilize the protein during the transit.[7][10] HGTD-P primarily acts in response to hypoxia by interacting with HIF-1α, which then triggers apoptotic cascades that result in the release of cytochrome C, induction of mitochondrial permeability transition, and activation of caspase-9 and 3.[5][7][8][10][11] In neuronal cells, it additionally stimulates mitochondrial release of
AIFM1, which then translocates to the nucleus to effect apoptosis, which indicates that it may participate in the
caspase-independent apoptotic pathway depending on cell type or organism.[5][9][10]
Clinical significance
Human growth and transformation-dependent protein (HGTD-P) is involved in intrinsic
apoptosis. Apoptosis, an ancient Greek word used to describe the "falling off" of petals from flowers or leaves from trees, is a highly regulated, evolutionarily conserved, and energy-requiring process by which activation of specific signaling cascades ultimately leads to cell death. An apoptotic cell undergoes structural changes including cell shrinkage, plasma membrane blebbing, nuclear condensation, and fragmentation of the
DNA and
nucleus. This is followed by fragmentation into apoptotic bodies that are quickly removed by
phagocytes, thereby preventing an
inflammatory response.[14] It is a mode of cell death defined by characteristic
morphological,
biochemical and
molecular changes. It was first described as a "shrinkage
necrosis", and then this term was replaced by apoptosis to emphasize its role opposite
mitosis in tissue kinetics. During apoptosis the cell decrease in size, loose contact with neighboring cells, and loose specialized surface elements such as microvilli and cell-cell junctions. A shift of fluid out of the cells causes cytoplasm condensation, which is followed by convolution of the nuclear and cellular outlines. In later stages of apoptosis the entire cell becomes fragmented, forming a number of plasma membrane-bounded apoptotic bodies which contain
nuclear and or
cytoplasmic elements. The ultrastructural appearance of necrosis is quite different, the main features being mitochondrial swelling, plasma membrane breakdown and cellular disintegration. Apoptosis occurs in many
physiological and
pathological processes. It plays an important role during
embryonal development as programmed cell death and accompanies a variety of normal involutional processes in which it serves as a mechanism to remove "unwanted" cells.
Due to its involvement in
hypoxia, HGTD-P has been implicated in cerebral ischemia and myocardial infarction, as well as numerous cancers, including cervical cancer and gastric cancer.[8][12][13] In the case of cervical cancer, HGTD-P is expressed in the early developmental stages and, thus, may prove useful as a diagnostic marker to control the spread of the cancer. Despite its proapoptotic function, HGTD-P has been observed to coordinate with HIF-1α to promote cell growth and proliferation under hypoxic conditions in cervical cancer.[12] In the case of hypoxia-ischemia brain damage, the
microRNA agomir, miR-139-5p, attenuates HGTD-P expression and brain damage, and has the therapeutic potential to treat hypoxia-ischemia brain damage.[11][15]
Interactions
HGTD-P has been shown to
interact with
Hsp90[7] and
VDAC.[8]HIF-1α is also known to bind to the hypoxia-responsive element of the HGTD-P
gene promoter and induce its transcription.[9]
^
abcdCho YE, Ko JH, Kim YJ, Yim JH, Kim SM, Park JH (Apr 2007). "mHGTD-P mediates hypoxic neuronal cell death via the release of apoptosis-inducing factor". Neuroscience Letters. 416 (2): 144–9.
doi:
10.1016/j.neulet.2007.01.073.
PMID17316997.
S2CID33662614.
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abcWebster KA, Graham RM, Thompson JW, Spiga MG, Frazier DP, Wilson A, Bishopric NH (2006). "Redox stress and the contributions of BH3-only proteins to infarction". Antioxidants & Redox Signaling. 8 (9–10): 1667–76.
doi:
10.1089/ars.2006.8.1667.
PMID16987020.
^
abCho YE, Kim JY, Kim YW, Park JH, Lee S (Jul 2009). "Expression and prognostic significance of human growth and transformation-dependent protein in gastric carcinoma and gastric adenoma". Human Pathology. 40 (7): 975–81.
doi:
10.1016/j.humpath.2008.12.007.
PMID19269009.