HAX-1: A Novel P-Body Protein

Abstract

HAX-1, a multifunctional protein involved in the regulation of apoptosis, cell migration, and calcium homeostasis, binds the 3¢ untranslated region motifs of specific transcripts. This suggests that HAX-1 plays a role in posttranscriptional regulation, at the level of mRNA stability/transport or translation. In this study, we analyze in detail HAX-1 colocalization with processing bodies (P-bodies) and its dependence on mRNA availability. Endogenous P-body markers DCP1 and Rck/p54 were shown to colocalize with endogenous HAX-1, but in case of the overexpressed proteins, only DCP1 displayed unperturbed colocalization with HAX-1. HAX-1 colocalization with DCP1 was observed in most of the cell lines studied, but its presence was not required for P-body formation, and its silencing caused an increase in P-body number. Preliminary mapping suggested that HAX-1 has more than one short P-body-targeting sequence. The pools of P-body-localized HAX-1 and cytosolic HAX-1 were demonstrated to dynamically exchange, suggesting steady flow of the protein. Active transcription was shown to be a factor in the localization of HAX-1 to P-bodies. Also, it was observed that HAX-1 localizes to some unidentified foci, which do not contain DCP1. In addition, it was demonstrated that HAX-1 status influences vimentin expression levels. Overall, HAX-1 was shown to colocalize with P-body markers and influence P-body number per cell in a manner dependent on mRNA availability. Presented data support the hypothesis that HAX-1 is involved in mRNA processing as an element of P-body interaction network.

The interactome of multifunctional HAX1 protein suggests its role in the regulation of energy metabolism, de-aggregation, cytoskeleton organization and RNA-processing

“…Accordingly, HAX1 has been implicated in numerous processes and activities, including the regulation of apoptosis [ 10–12 ], cell migration [ 13–15 ], regulation of calcium concentration in the endoplasmic reticulum [ 16 , 17 ], actin cytoskeleton reorganization [ 18 ], granulocyte differentiation [ 19 , 20 ], B-cell signaling [ 21 , 22 ], endocytosis [ 15 ], adhesion [ 14 , 23 ] and ubiquitination [ 24 ]. It was also detected not only in the mitochondria, which represents its predominant localization [ 25 , 26 ], but also in the endoplasmic reticulum [ 16 ], on the leading edge of lamellipodia [ 27 ], in P-bodies [ 28 ] and in the nucleus [ 29 , 30 ]. Adding to the complexity of the role of HAX1 in the cell, this protein was demonstrated to bind mRNA and influence its stability [ 29–31 ].…”

Grb7 and Hax1 may colocalize partially to mitochondria in EGF‐treated SKBR3 cells and their interaction can affect Caspase3 cleavage of Hax1

“…The immunofluorescence confocal images in this study indicate that many locations of Grb7/Hax1 colocalization in SKBR3 cells remain inconclusively identified. Interestingly, Zayat et al (2015) also noted the presence of unidentified granular bodies containing Hax1 that were not P-bodies (Zayat et al, 2015). In that study, HeLa cells treated with puromycin, and primary neuronal cells, both displayed two types of Hax1 cytoplasmic granules.…”

“…Interestingly, Zayat et al . () also noted the presence of unidentified granular bodies containing Hax1 that were not P‐bodies (Zayat et al ., ). In that study, HeLa cells treated with puromycin, and primary neuronal cells, both displayed two types of Hax1 cytoplasmic granules.…”

HAX1 mutation positive children presenting with haemophagocytic lymphohistiocytosis

“…The functions of HAX1 and its mechanism of action have not been fully elucidated. The protein is implicated in the regulation of several vital cellular processes, including apoptosis, cell migration, calcium homeostasis and mRNA regulation (Germeshausen et al , ; Zayat et al , ). HAX1 encodes the HCLS1‐associated protein X‐1, a mitochondrion ‐ associated anti‐apoptotic protein that is critical for maintaining the inner mitochondrial membrane potential and protecting myeloid cells from apoptosis (Klein et al , ).…”