ErbB4 Expression in Neural Progenitor Cells (ST14A) Is Necessary to Mediate Neuregulin-1β1-induced Migration

Abstract

Activation of the receptor tyrosine kinase ErbB4 leads to various cellular responses such as proliferation, survival, differentiation, and chemotaxis. Two pairs of naturally occurring ErbB4 isoforms differing in their juxtamembrane (JMa/JMb) and C termini (cyt1/cyt2) have been described. To examine the role of ErbB4 in neuron migration, we cloned and stably transfected each of the four ErbB4 isoforms in ST14A cells (a neural progenitor cell line derived from the striatum of embryonic day 14 rats) endogenously expressing the other members of the ErbB family: ErbB1, ErbB2, and ErbB3. Using immunoprecipitation assays, we showed that the neuregulin-1␤1 (NRG1␤1) stimulus induced ErbB4 tyrosine phosphorylation and phosphatidylinositol 3-kinase (PI3K) recruitment and activation (as demonstrated by Akt phosphorylation) either directly (ErbB4 cyt1 isoform) or indirectly (ErbB4 cyt2 isoform). We examined the ability of the four ErbB4 isoforms to induce chemotaxis and cell proliferation in response to NRG1␤1 stimulation. Using migration assays, we observed that only ErbB4-expressing cells stimulated with NRG1␤1 showed a significant increase in migration, whereas the growth rate remained unchanged. Additional assays showed that inhibition of PI3K (but not of phospholipase C␥) dramatically reduced migratory activity. Our data show that ErbB4 signaling via PI3K activation plays a fundamental role in controlling NRG1␤1-induced migration.The ErbB receptor family consists of four receptor tyrosine kinases named the epidermal growth factor (EGF) 1 receptor, ErbB2, ErbB3, and ErbB4 (reviewed in Ref. 1). Ligand-dependent activation of ErbB receptors results in homo-or heterodimerization, which stimulates receptor trans-phosphorylation on cytoplasmic tyrosine residues, creating binding sites for adaptor or enzymatic proteins. EGF receptor and ErbB4 homodimers are active kinases in the absence of coreceptors, whereas ErbB3 (which has little or no intrinsic tyrosine kinase activity) and ErbB2 (for which no ligand has been identified) necessitate coreceptor interaction for signal transduction (2). Thus, whereas ErbB2 and ErbB3 are limited to heterodimerization, the EGF receptor and ErbB4 can be activated by either homo-or heterodimerization.An interesting ErbB4 feature (recently reviewed in Ref.3) is the existence of isoforms generated by alternative splicing (4). One isoform pair (5) is characterized by alternative splicing of exons located in the extracellular juxtamembrane region conferring (JMa), or not (JMb), susceptibility to proteolytic cleavage (6) by a member of the ADAM (a disintegrin and metalloprotease) family, the tumor necrosis factor-␣-converting enzyme (7). ErbB4 proteolytic cleavage produces a membraneassociated 80-kDa fragment that can be degraded by proteasome activity following polyubiquitination (8) or that can be the substrate for subsequent ␥-secretase cleavage, which releases the cytoplasmic domain from the membrane and allows, intriguingly, nuclear translocation of a fragment (9, 10) that can act as cotranscrip...

Neuregulin1/ErbB4-induced migration in ST14A striatal progenitors: calcium-dependent mechanisms and modulation by NMDA receptor activation

“…As expected [6], NRG1 does not enhance migration of wt ST14A, both when administered alone or in the presence of NMDA.…”

“…The present work is a first attempt to address this issue in a simplified in vitro model of neural progenitors, the ST14A cell line [23], in which NRG1/ErbB4 mediated migration has been previously characterized [6,24]. As expected from the expression data, we show that NMDA induces small Ca 2+ signals in ErbB4-transfected ST14A cells.…”

“…Results clearly show that wt ST14A cells have a low basal intrinsic motility that is not altered by the presence of NMDA (Figure 1C). On the other hand, NMDA could have no effect per se in ST14A cell migration, and have instead an effect when added together with other molecules, such as members of the neuregulin family, and specifically NRG1, that has been shown to promote ErbB4 mediated neuronal migration [6-8]. Wt ST14A cells do not express ErbB4; however, they express other ErbB receptors, which could mediate a NRG1-induced response in the presence of NMDA.…”

“…Our laboratory has previously shown that ST14A clones stably transfected with different ErbB4 isoforms show a variable degree of increased migratory activity when stimulated by NRG1, depending on the specific ErbB4 isoform [6]. Since there are no data in the literature comparing the interactions of different ErbB4 isoforms with NMDARs, we used the two ErbB4 expressing clones showing the highest increase in migration following NRG1 stimulation.…”

“…Receptor-ligand interaction induces the homo- or heterodimerization with other members of the ErbB receptor family, which in turn results in the activation of several intracellular signalling pathways and the induction of cellular responses including migration of neuronal precursor cells [4-6]. In vivo studies demonstrate that the NRG1/ErbB4 system is involved in tangential migration of olfactory bulb (OB) interneuron precursors in the rostral migratory stream (RMS) [7] and of cortical interneuron precursors migrating from the ventral telencephalon [8].…”