Functional Analysis of B144/LST1: A Gene in the Tumor Necrosis Factor Cluster That Induces Formation of Long Filopodia in Eukaryotic Cells

LST1/A Is a Myeloid Leukocyte-specific Transmembrane Adaptor Protein Recruiting Protein Tyrosine Phosphatases SHP-1 and SHP-2 to the Plasma Membrane

“…ing results on the expression pattern of LST1 have been reported (1,3,5,7,8). Thus, we revisited this issue using a quantitative comparison of LST1/A expression levels in various cell subsets and tissues at both the mRNA and protein levels.…”

“…Indeed, the LST1/A protein structure exhibits key features of a TRAP (14). First, it possesses only a very short extracellular domain (including a possibly dimerizing cysteine), followed by a transmembrane domain and a comparatively larger cytoplasmic tail (7,8). Second, the protein lacks any domain with predicted enzymatic activity.…”

“…However, it remains unclear how many LST1 splice variants really exist at the protein level. So far, the only protein product clearly detected in vivo is encoded by the LST1/A isoform, the only isoform conserved between human and mouse (7,8).…”

“…Several studies reported enrichment or specific expression of LST1 in leukocytes or leukocyte-rich tissues (1,3,7), whereas others indicated that the expression of LST1 is relatively ubiquitous (5,8). Moreover, it seems that production of particular isoforms could be differentially regulated, which further complicates expression analysis (5,9).…”

“…A single published phenotypic study reported that overexpression of LST1/A in various human cell lines resulted in the formation of filopodialike structures (7). Nevertheless, no molecular mechanism explaining how LST1 could induce the changes in cell morphology has been proposed, and thus, the physiological function of LST1/A is still unknown.…”