Erythroid spectrin is the predominant component of the twodimensional protein network called the membrane skeleton, underlying the lipid bilayer of red cells (for recent reviews, seeRefs. 1-3). Formation of the membrane skeleton involves multiple protein-protein interactions among integral membrane proteins. Interactions of spectrin with other membrane proteins such as ankyrin, protein 4.1, and adducin provide a linkage of spectrin either to the plasma membrane or among spectrin tetramers. Many hereditary anemia mutations affect interactions of these integral membrane proteins, resulting in increased fragility and shortened lifespan of erythrocytes. In hereditary elliptocytosis and pyropoikilocytosis, the mutations have been localized in the ␣-and ␤-subunits of spectrin (reviewed in Refs. 4 and 5). Many of these proteins, including spectrin, which were first identified in red cells, have isoforms expressed in nonerythroid cells, but the structure and regulatory processes of the nonerythroid membrane skeleton are less well understood (reviewed in Refs. 1-3, 6, and 7). Functional differences between the membranes of erythroid and nonerythroid cells argue against the simple erythrocyte model of the membrane skeleton. Major differences between the erythroid model and other cells include differences in the expression of spectrin (8 -11) and ankyrin isoforms (12-15) (reviewed in Ref.16), interactions of spectrin and ankyrin with additional proteins (17-21), localization of spectrin in the cytoplasm as well as in the plasma membrane (10,11,22), and the potential for dramatic rearrangements of spectrin's cellular location (23, 24) (reviewed in Refs. 2 and 7).Several studies have demonstrated that both erythroid and nonerythroid spectrins are expressed in brain tissue (8 -11, 25). Neuronal compartmentalization of brain spectrin isoforms into axons and presynaptic terminals (nonerythroid spectrin) and into cell bodies and dendrites (erythroid spectrin) (10, 25) suggests that brain spectrin isoforms may perform related but distinct functions in neuronal cells. It has been suggested that nonerythroid spectrin performs a more general, constitutive role, while erythroid spectrin takes part in more specialized activities of differentiated cells (26). The ␣-subunit of erythroid spectrin, ␣I (27), 1 and the ␣-subunit of nonerythroid spectrin, ␣II (28, 29), each contains a unique SH3 2 domain. Distinct protein interactions are likely to involve these domains, and they may be important for specific distribution and specialized roles of brain spectrin isoforms.

SummaryIn fibroblasts, platelet-derived growth factor (PDGF) stimulates macropinocytosis and PI 3-kinase (PI3K)-dependent phosphorylation of Akt, leading to activation of mTORC1, a protein complex controlling metabolism and cell growth. PIP3, the phosphoinositide product of PI3K that activates Akt, is frequently concentrated within the macropinocytic cups of growth factorstimulated cells, which suggests that cup structure enhances phosphorylation of Akt by facilitating PI3K activity. However, inhibitors of the cytoskeleton which block cup formation do Stimulation with low concentrations of PDGF elicited lower levels of Akt phosphorylation, which, like responses to EGF, were inhibited by nocodazole. These results indicate that when receptor signaling generates low levels of PI3K activity, CDR facilitate local amplification of PI3K, PIP3 synthesis and phosphorylation of Akt.All rights reserved. No reuse allowed without permission.

The cytoplasmic domain of the beta amyloid precursor protein (betaAPP) may play a role in cellular events that lead to the secretion of the Abeta peptide, the major constituent of amyloid plaques found in the brains of individuals affected by Alzheimer's disease, by interacting with cellular factors involved in betaAPP function or processing. In order to elucidate the structural basis of cytoplasmic domain activity, the conformations adopted in solution by a peptide containing the 47-residue C-terminal sequence of betaAPP have been investigated by NMR and CD spectroscopy. The peptide does not have a stable tertiary structure, but local regions of the polypeptide chain populate defined conformations. In particular, the amino acid sequences TPEE and NPTY form type I reverse turns. These structured regions correspond to sequences within the cytoplasmic domain implicated in the biological activity of betaAPP.

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280 Background: Prostate cancer is characterized by heterogeneity of mechanisms which are poorly understood but pointing to epithelial plasticity as the key mechanism in progression to metastatic disease. ABI1, a member of WAVE complex and actin cytoskeleton regulator and adaptor protein, is proposed to act as tumor suppressor in prostate cancer, but the mechanism of tumor progression due to Abi1 loss is not clear. Methods: To address Abi1’s role in prostate cancer we used CRISPR-based gene editing and retroviral expression to manipulate Abi1 levels in prostate cancer cell lines. Levels of Abi1 expression in prostate organoid tumor cell lines were evaluated by Western blotting and/or RNA sequencing. Association of Abi1 loss with tumor grade was evaluated by immunohistochemistry. Results: Abi1 expression is downregulated in tumor organoid cell lines from metastatic bone and lymph node biopsies. Moreover, low Abi1 expression is associated with high-grade prostate tumors (GG3 or higher, p < 0.001). Disruption of Abi1 gene in a benign prostate epithelial cell line RWPE-1 resulted in a gain of invasive phenotype, which is characterized by loss of cell-cell adhesion markers and increased migratory ability of RWPE-1 Abi1 KO spheroids. Through RNA sequencing and protein expression analysis we discovered that Abi1 loss leads to activation of non-canonical WNT signaling and EMT pathways, which are rescued by re-expression of Abi1. Furthermore, increase in STAT3 phosphorylation upon Abi1 inactivation and evidence for high affinity interaction of FYN-SH2 domain with Abi1 pY421 support the model that Abi1 acts as a gatekeeper of the non-canonical WNT-EMT pathway activation downstream from FZD2 receptor. The gene expression profile of Abi1-EMT-WNT pathway overlaps with the reported gene signature of high-risk prostate tumors. Conclusions: Abi1 contributes to prostate cancer progression and epithelial plasticity through regulation of EMT-WNT pathways. Understanding of Abi1’s role may provide more mechanistic understanding of prostate cancer tumor progression.