Truncated activin type II receptor inhibits erythroid differentiation in K562 cells

Abstract

Two receptor serine/threonine kinases (types I and II) have been identified as signaling transducing activin receptors. We studied the possibility of inhibiting activin A-dependent differentiation in K562 cells, using a dominant negative mutant of type II receptor. A vector was constructed expressing activin type II truncated receptor (ActRIIa) that lacks the cytoplasmic kinase domain. Since activin type I and II receptors form heteromeric complexes for signaling, the mutant receptors compete for binding to endogenous receptors, hence acting in a dominant negative fashion. K562 cells were stably transfected with ActRIIa, and independent clones were expanded. The truncated cDNA was integrated into the genome of the transfectants, as shown by polymerase chain reaction; and the surface expression of truncated receptors was shown by affinity cross-linking with (125)I-activin A. In wild-type K562 cells, activin A induced erythroid differentiation and cells started to express hemoglobins. In transfected cells expressing ActRIIa, the induction of erythroid differentiation was abrogated and less than 10% of cells were hemoglobin-containing cells after culture with activin A. Further transfection with wild-type type II receptors rescued the mutant phenotype of these transfectants, indicating that the effect of ActRIIa is dominant negative. In addition, phosphorylation of the cytoplasmic kinase domain of the type II receptor in vitro confirms the autophosphorylation of this portion of the receptor. Therefore, induction of erythroid differentiation in vitro is mediated through the cell surface activin receptor, and interference with this receptor signaling inhibits this process of differentiation in K562 cells.

p27KIP1 and GATA-1 are potential downstream molecules in activin A-induced differentiation and apoptosis pathways in CML cells

“…Furthermore, co-stimulation with activin A and erythropoietin, a survival factor for erythroid cells and a downstream target of GATA-1 promoter (33,34), overrode activin A-induced apoptosis and stimulated erythroid differentiation in KU812 cells (23). Although the GenBank database analysis did not show the putative Smad binding site in the human GATA-1 promoter region, there have been many studies on the regulation of erythropoiesis by the TGF-ß superfamily (35)(36)(37)(38)(39). In addition, expression of GATA-1 also activates the induction of several erythroid-related genes (40).…”

Bone morphogenetic protein and activin signaling in colorectal cancer

“…Somatic frameshift mutations in ACVR1 have been described in pancreatic cancer [44], and somatic mutation and loss of heterozygosity at the ACVR2 locus has been described in pancreatic carcinoma [27]. Mutated ACVR2 abolishes activin-mediated erythroid differentiation [45].…”