SGIP1α, but Not SGIP1, is an Ortholog of FCHo Proteins and Functions as an Endocytic Regulator

Src homology 3-domain growth factor receptor-bound 2-like interacting protein 1 (SGIP1), originally known as a regulator of energy homeostasis, was later found to be an ortholog of Fer/Cip4 homology domain-only (FCHo) proteins and to function during endocytosis. SGIP1α is a longer splicing variant in mouse brains that contains additional regions in the membrane phospholipid-binding domain (MP) and C-terminal region, but functional consequences with or without additional regions between SGIP1 and SGIP1α remain elusive. Moreover, many previous studies have either inadvertently used SGIP1 instead of SGIP1α or used the different isoforms with or without additional regions indiscriminately, resulting in further confusion. Here, we report that the additional region in the MP is essential for SGIP1α to deform membrane into tubules and for homo-oligomerization, and SGIP1, which lacks this region, fails to perform these functions. Moreover, only SGIP1α rescued endocytic defects caused by FCHo knock-down. Thus, our results indicate that SGIP1α, but not SGIP1, is the functional ortholog of FCHos, and SGIP1 and SGIP1α are not functionally redundant. These findings suggest that caution should be taken in interpreting the role of SGIP1 in endocytosis.

The intramolecular allostery of GRB2 governing its interaction with SOS1 is modulated by phosphotyrosine ligands

Growth factor receptor-bound protein 2 (GRB2) is a trivalent adaptor protein and a key element in signal transduction. It interacts via its flanking nSH3 and cSH3 domains with the proline-rich domain (PRD) of the RAS activator SOS1 and via its central SH2 domain with phosphorylated tyrosine residues of receptor tyrosine kinases (RTKs; e.g., HER2). The elucidation of structural organization and mechanistic insights into GRB2 interactions, however, remain challenging due to their inherent flexibility. This study represents an important advance in our mechanistic understanding of how GRB2 links RTKs to SOS1. Accordingly, it can be proposed that (1) HER2 pYP-bound SH2 potentiates GRB2 SH3 domain interactions with SOS1 (an allosteric mechanism); (2) the SH2 domain blocks cSH3,enabling nSH3 to bind SOS1 first before cSH3 follows (an avidity-based mechanism); and (3) the allosteric behavior of cSH3 to other domains appears to be unidirectional, although there is an allosteric effect between the SH2 and SH3 domains.

Regulation of Phosphoinositide Levels in the Retina by Protein Tyrosine Phosphatase 1B and Growth Factor Receptor-Bound Protein 14

Protein tyrosine kinases and protein phosphatases play a critical role in cellular regulation. The length of a cellular response depends on the interplay between activating protein kinases and deactivating protein phosphatases. Protein tyrosine phosphatase 1B (PTP1B) and growth factor receptor-bound protein 14 (Grb14) are negative regulators of receptor tyrosine kinases. However, in the retina, we have previously shown that PTP1B inactivates insulin receptor signaling, whereas phosphorylated Grb14 inhibits PTP1B activity. In silico docking of phosphorylated Grb14 and PTP1B indicate critical residues in PTP1B that may mediate the interaction. Phosphoinositides (PIPs) are acidic lipids and minor constituents in the cell that play an important role in cellular processes. Their levels are regulated by growth factor signaling. Using phosphoinositide binding protein probes, we observed increased levels of PI(3)P, PI(4)P, PI(3,4)P2, PI(4,5)P2, and PI(3,4,5)P3 in PTP1B knockout mouse retina and decreased levels of these PIPs in Grb14 knockout mouse retina. These observations suggest that the interplay between PTP1B and Grb14 can regulate PIP metabolism.

The Challenges and Strategies of Antisense Oligonucleotide Drug Delivery

Antisense oligonucleotides (ASOs) are used to selectively inhibit the translation of disease-associated genes via Ribonuclease H (RNaseH)-mediated cleavage or steric hindrance. They are being developed as a novel and promising class of drugs targeting a wide range of diseases. Despite the great potential and numerous ASO drugs in preclinical research and clinical trials, there are many limitations to this technology. In this review we will focus on the challenges of ASO delivery and the strategies adopted to improve their stability in the bloodstream, delivery to target sites, and cellular uptake. Focusing on liposomal delivery, we will specifically describe liposome-incorporated growth factor receptor-bound protein-2 (Grb2) antisense oligodeoxynucleotide BP1001. BP1001 is unique because it is uncharged and is essentially non-toxic, as demonstrated in preclinical and clinical studies. Additionally, its enhanced biodistribution makes it an attractive therapeutic modality for hematologic malignancies as well as solid tumors. A detailed understanding of the obstacles that ASOs face prior to reaching their targets and continued advances in methods to overcome them will allow us to harness ASOs’ full potential in precision medicine.

EGF-Activated Grb7 Confers to STAT3-Mediated EPHA4 Gene Expression in Regulating Lung Cancer Progression

Growth factor receptor bound protein-7 (Grb7) is a multi-domain signaling adaptor protein that regulates various cellular functions acting as an adaptor protein in relaying signal transduction. Although several studies indicated that Grb7 amplifies EGFR-mediated signaling in cancers, the detailed regulatory mechanism of whether and how Grb7 is involved in EGFR-mediated lung cancer progression remains unclear. Here, we demonstrate that EGF-regulated Grb7 phosphorylation promotes lung cancer progression through phosphorylation of STAT3. Intrinsically, EGF/EGFR signal is required for the formation of Grb7/STAT3 complex as well as its nuclear accumulation. Once in the nucleus, STAT3 interacts with EPHA4 promoter, which in turn affects the gene expression level of EPHA4 through transcriptional regulation. Functionally, EphA4 together with EGFR promotes cancer migration, proliferation, and anchorage-independent growth. Our study reveals a novel mechanism in which Grb7 contribute to lung cancer malignancies through its interaction with STAT3 that leads to sequential regulation of EPHA4 gene expression in an EGF/EGFR signal-dependent manner.

High Expression of Growth Factor Receptor-bound Protein 14 Predicts Clinical Progression and Poor Prognosis in Patients with Lung Adenocarcinoma

Background: Growth factor receptor-bound protein 14 (Grb14) is an adaptor molecule of the Grb7/10/14 family with a characteristic “between PH and SH2” (BPS) domain that serves to tightly bind tyrosine kinases. Previous studies have demonstrated that Grb14 upregulation may be used as a marker of proliferation, invasion and malignant cell growth in tumors. The overexpression of Grb14 has also been reported to be associated with a poor prognosis in cancer patients. However, the clinical significance of Grb14 in lung adenocarcinoma has not yet been fully elucidated.Methods: Grb14 protein expression in human lung adenocarcinoma and noncancerous lung tissues was detected by immunohistochemistry analyses. Then, the associations of Grb14 expression with clinicopathological features and clinical outcomes of lung cancer patients were validated by analyzing a microarray-based TCGA dataset at the mRNA level and statistically evaluating the results.Results: Immunohistochemistry and dataset analyses revealed that Grb14 expression was significantly increased in lung adenocarcinoma tissues compared with noncancerous lung tissues [immunoreactivity score (IRS): lung adenocarcinoma, 6.07±1.01 vs benign, 4.80±1.22, P<0.001]. Additionally, as revealed by analysis of the dataset, the upregulation of Grb14 mRNA expression in the lung adenocarcinoma tissues was significantly correlated with poor overall survival (P<0.001). Furthermore, univariate analysis revealed that higher pathological stage [hazard ratio (HR), 1.925, 95% CI, 0.912-6.301; P<0.05], higher tumor stage (HR, 2.436, 95% CI, 1.659-5.551; P<0.001), higher surgical margin resection status (HR, 3.035, 95% CI, 1.305-37.51; P<0.01) and prior diagnosis status (HR, 0.4893, 95% CI, 0.1818-0.8197; P<0.01) were independent predictors for a shorter survival. Multivariate analysis also revealed that higher pathological stage (HR, 3.730, 95% CI, 1.784-7.796; P<0.01), higher surgical margin resection status (HR, 6.914, 95% CI, 2.063-23.171; P<0.01) and prior diagnosis status were related to a shorter survival. Conclusion: Our data suggest that elevated Grb14 expression plays an important role in the progression of lung adenocarcinoma. More importantly, the increased expression of Grb14 may efficiently predict poor survival in lung adenocarcinoma patients.