BackgroundHuman umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) have been shown to prevent brain damage and improve neurocognition following intraventricular hemorrhage (IVH). However, the molecular mechanisms underlying the effects of hUCB-MSCs are still elusive. Thus, as the hippocampus is essential for learning, memory, and cognitive functions and is intimately involved in the ventricular system, making it a potential site of IVH-induced injury, we determined the molecular basis of the effects of hUCB-derived MSCs on hippocampal neurogenesis and the recovery of hippocampal neural circuits after IVH in a rodent model.MethodsWe inflicted severe IVH injury on postnatal day 4 (P4) in rats. After confirmation of successful induction of IVH using MRI (P5), intracerebroventricular administration of MSCs (ICV-MSC) was performed at 2 days post-injury (P6). For hippocampal synaptic determination, a rat entorhinal-hippocampus (EH) organotypic slice co-culture (OSC) was performed using day 3 post-IVH brains (P7) with or without ICV-MSCs. A similar strategy of experiments was applied to those rats receiving hUCB-MSC transfected with BDNF-Si-RNA for knockdown of BDNF or scrambled siRNA controls after IVH. The molecular mechanism of the MSCs effects on neurogenesis and the attenuation of neuron death was determined by evaluation of BDNF-TrkB-Akt-CREB signaling axis.ResultsWe showed that treatment with hUCB-MSCs attenuated neuronal loss and promoted neurogenesis in the hippocampus, an area highly vulnerable to IVH-induced brain injury. hUCB-MSCs activate BDNF-TrkB receptor signaling, eliciting intracellular activation of Akt and/or Erk and subsequent phosphorylation of CREB, which is responsible for promoting rat BDNF transcription. In addition to the beneficial effects of neuroprotection and neurogenesis, hUCB-MSCs also contribute to the restoration of impaired synaptic circuits in the hippocampus and improve neurocognitive functions in IVH-injured neonatal rat through BDNF-TrkB-CREB signaling axis activation.ConclusionsOur data suggest that hUCB-MSCs possess therapeutic potential for treating neuronal loss and neurocognitive dysfunction in IVH through the activation of intracellular TrkB-CREB signaling that is invoked by hUCB-MSC-secreted BDNF.Electronic supplementary materialThe online version of this article (10.1186/s13287-018-1052-5) contains supplementary material, which is available to authorized users.

The long isoform of ErbB3 binding protein 1 (Ebp1), p48, strongly promotes tumorigenesis of glioblastoma, accelerating cell proliferation and transformation, while the short isoform, p42, which lacks the N-terminal 54 amino acids, inhibits tumor growth. However, it is unclear if the N-terminal domain of p48 regulates the oncogenic function of p48. Here, we show that p48, but not p42, interacts with cyclin-dependent kinase 2 (CDK2) through its N-terminal domain, resulting in the specific phosphorylation of serine 34 of p48. Overexpression of wild-type p48 greatly enhanced tumor cell growth, whereas phospho-ablated mutant S34A of p48, which is mutated at the CDK2 phosphorylation site, antagonizes cell proliferation and transformation. Moreover, phospho-ablated mutant S34A abrogated the ability of p48 to accelerate tumor cell growth in a mouse engraft model. Thus, our findings indicate that p48Ebp1 acts as an oncoprotein through selective interaction and/or modification of the N-terminal domain that does not exist in its short isoform p42.

The different functions of the two isoforms of ErbB3 binding protein 1 (Ebp1), p48 and p42, have recently become the focus of interest as they reveal contradictory roles in cell growth promoting ability. The conformational change that crystal structure of p42 was shown to lack a helices at the amino-terminus present in p48 represents the differential binding partners and protein modifications of two Ebp1 isoforms. N-terminal specific phosphorylation by CDK2 and deregulation of the p53 tumor suppressor through specific interaction with HDM2 and Akt activation is postulated to contribute to p48-mediated tumorigenesis. The short isoform p42 Ebp1, which is actual binding partner of ErbB3 has been implicated as a tumor suppressor with many binding partners such as Rb, HDAC2, Sin3A and the p85 subunit of PI3K with HSP70/CHIP, inhibiting its own antiproliferative activity or inhibiting PI3K activity. The aim of the current review is to provide a summary on distinctive cellular functions of two Ebp1 proteins and their molecular partners that might be responsible for the unique functions of each isoform of Ebp1.ErbB3 binding protein 1 (Ebp1) was originally identified as an ErbB3 receptor-binding protein 1 and is the human homolog of mouse p38-2G4, which has been shown to be cell cycle-regulated. 2 Although Ebp1 was originally identified via its interaction with ErbB3, 1 Ebp1 is ubiquitously expressed in all tissues and cells, including cells that do not express the ErbB3 receptor. 3 Ebp1 is evolutionarily conserved, 2,4 suggesting that it may function as a general signaling molecule. PA2G4 encodes two alternatively spliced Ebp1 isoforms, p48 and p42, that are transcribed into two mRNA transcripts; interestingly, however, PA2G4 harbors three in-frame ATG codons. 5 Translation is initiated at the first ATG codon for p48, which migrates at an apparent molecular weight of 48 kDa and is 54 amino acids longer than p42 at the Nterminus. p42 translation begins at the third ATG codon, resulting in the omission of a 29 nucleotide exon, which eliminates the second ATG in the p48 mRNA. The resultant protein migrates at an apparent molecular weight of 42 kDa by SDS/PAGE. 5 The longer form, p48, localizes in both the cytoplasm and the nucleolus and suppresses apoptosis, whereas the shorter form, p42, resides predominantly in the cytoplasm and promotes cell differentiation. 5 Ebp1 binds ribosomes and dsRNA and is also a component of cytoplasmic bcl-2 messenger ribonucleoprotein (mRNP). 6,7 Recently, we showed that p48 Ebp1 associates with nuclear Akt and prevents apoptosis, which is mediated by PKC-d-triggered phosphorylation on S360. 8 Ebp1 has also been shown to regulate plant growth. Manipulating the expression level of stEBP1 (homolog of mammalian p48) affects the organ growth of transgenic plants. Specifically, increased levels are associated with increased growth, whereas decreased levels are associated with decreased growth; these effects are dose dependent. During the early stages of organ development, stEBP1 promotes cell prol...