The intrinsic substrate specificity of the human tyrosine kinome.

Phosphorylation of proteins on tyrosine (Tyr) residues evolved in metazoan organisms as a mechanism of coordinating tissue growth1. Multicellular eukaryotes typically have more than 50 distinct protein Tyr kinases that catalyse the phosphorylation of thousands of Tyr residues throughout the proteome1-3. How a given Tyr kinase can phosphorylate a specific subset of proteins at unique Tyr sites is only partially understood4-7. Here we used combinatorial peptide arrays to profile the substrate sequence specificity of all human Tyr kinases. Globally, the Tyr kinases demonstrate considerable diversity in optimal patterns of residues surrounding the site of phosphorylation, revealing the functional organization of the human Tyr kinome by substrate motif preference. Using this information, Tyr kinases that are most compatible with phosphorylating any Tyr site can be identified. Analysis of mass spectrometry phosphoproteomic datasets using this compendium of kinase specificities accurately identifies specific Tyr kinases that are dysregulated in cells after stimulation with growth factors, treatment with anti-cancer drugs or expression of oncogenic variants. Furthermore, the topology of known Tyr signalling networks naturally emerged from a comparison of the sequence specificities of the Tyr kinases and the SH2 phosphotyrosine (pTyr)-binding domains. Finally we show that the intrinsic substrate specificity of Tyr kinases has remained fundamentally unchanged from worms to humans, suggesting that the fidelity between Tyr kinases and their protein substrate sequences has been maintained across hundreds of millions of years of evolution.

CIS is a potent checkpoint in NK cell-mediated tumor immunity.

The detection of aberrant cells by natural killer (NK) cells is controlled by the integration of signals from activating and inhibitory ligands and from cytokines such as IL-15. We identified cytokine-inducible SH2-containing protein (CIS, encoded by Cish) as a critical negative regulator of IL-15 signaling in NK cells. Cish was rapidly induced in response to IL-15, and deletion of Cish rendered NK cells hypersensitive to IL-15, as evidenced by enhanced proliferation, survival, IFN-γ production and cytotoxicity toward tumors. This was associated with increased JAK-STAT signaling in NK cells in which Cish was deleted. Correspondingly, CIS interacted with the tyrosine kinase JAK1, inhibiting its enzymatic activity and targeting JAK for proteasomal degradation. Cish(-/-) mice were resistant to melanoma, prostate and breast cancer metastasis in vivo, and this was intrinsic to NK cell activity. Our data uncover a potent intracellular checkpoint in NK cell-mediated tumor immunity and suggest possibilities for new cancer immunotherapies directed at blocking CIS function.

Interaction domains of Sos1/Grb2 are finely tuned for cooperative control of embryonic stem cell fate.

Metazoan evolution involves increasing protein domain complexity, but how this relates to control of biological decisions remains uncertain. The Ras guanine nucleotide exchange factor (RasGEF) Sos1 and its adaptor Grb2 are multidomain proteins that couple fibroblast growth factor (FGF) signaling to activation of the Ras-Erk pathway during mammalian development and drive embryonic stem cells toward the primitive endoderm (PrE) lineage. We show that the ability of Sos1/Grb2 to appropriately regulate pluripotency and differentiation factors and to initiate PrE development requires collective binding of multiple Sos1/Grb2 domains to their protein and phospholipid ligands. This provides a cooperative system that only allows lineage commitment when all ligand-binding domains are occupied. Furthermore, our results indicate that the interaction domains of Sos1 and Grb2 have evolved so as to bind ligands not with maximal strength but with specificities and affinities that maintain cooperativity. This optimized system ensures that PrE lineage commitment occurs in a timely and selective manner during embryogenesis.

Non-histone protein methylation as a regulator of cellular signalling and function.

Methylation of Lys and Arg residues on non-histone proteins has emerged as a prevalent post-translational modification and as an important regulator of cellular signal transduction mediated by the MAPK, WNT, BMP, Hippo and JAK-STAT signalling pathways. Crosstalk between methylation and other types of post-translational modifications, and between histone and non-histone protein methylation frequently occurs and affects cellular functions such as chromatin remodelling, gene transcription, protein synthesis, signal transduction and DNA repair. With recent advances in proteomic techniques, in particular mass spectrometry, the stage is now set to decode the methylproteome and define its functions in health and disease.

SnapShot: Lysine Methylation beyond Histones.

Lysine methylation is a prevalent post-translational modification (PTM) used by the cell to reversibly regulate protein function. Although it has been extensively studied in the context of histones and the associated chromatin, the remaining methyllysine proteome remains largely unexplored. This SnapShot provides an overview of the current state of lysine methylation research and its emergence as a dynamic PTM occurring on histone and non-histone proteins.

Proteomic and Phosphoproteomic Reprogramming in Epithelial Ovarian Cancer Metastasis.

Epithelial ovarian cancer (EOC) is a high-risk cancer presenting with heterogeneous tumors. The high incidence of EOC metastasis from primary tumors to nearby tissues and organs is a major driver of EOC lethality. We used cellular models of spheroid formation and readherence to investigate cellular signaling dynamics in each step toward EOC metastasis. In our system, adherent cells model primary tumors, spheroid formation represents the initiation of metastatic spread, and readherent spheroid cells represent secondary tumors. Proteomic and phosphoproteomic analyses show that spheroid cells are hypoxic and show markers for cell cycle arrest. Aurora kinase B abundance and downstream substrate phosphorylation are significantly reduced in spheroids and readherent cells, explaining their cell cycle arrest phenotype. The proteome of readherent cells is most similar to spheroids, yet greater changes in the phosphoproteome show that spheroid cells stimulate Rho-associated kinase 1 (ROCK1)-mediated signaling, which controls cytoskeletal organization. In spheroids, we found significant phosphorylation of ROCK1 substrates that were reduced in both adherent and readherent cells. Application of the ROCK1-specific inhibitor Y-27632 to spheroids increased the rate of readherence and altered spheroid density. The data suggest ROCK1 inhibition increases EOC metastatic potential. We identified novel pathways controlled by Aurora kinase B and ROCK1 as major drivers of metastatic behavior in EOC cells. Our data show that phosphoproteomic reprogramming precedes proteomic changes that characterize spheroid readherence in EOC metastasis.

Examining lack of referrals to heart valve specialists as mechanisms of potential underutilization of aortic valve replacement.

BACKGROUND: Recent studies suggest that aortic valve replacement (AVR) remains underutilized. AIMS: Investigate the potential role of non-referral to heart valve specialists (HVS) on AVR utilization. METHODS: Patients with severe aortic stenosis (AS) between 2015 and 2018, who met class I indication for intervention, were identified. Baseline data and process-related parameters were collected to analyze referral predictors and evaluate outcomes. RESULTS: Among 981 patients meeting criteria AVR, 790 patients (80.5%) were assessed by HVS within six months of index TTE. Factors linked to reduced referral included increasing age (OR: 0.95; 95% CI: 0.94-0.97; P < .001), unmarried status (OR: 0.59; 95% CI: 0.43-0.83; P = .002) and inpatient TTE (OR: 0.27; 95% CI: 0.19-0.38; P < .001). Conversely, higher hematocrit (OR: 1.13; 95% CI: 1.09-1.16; P < .001) and eGFR (OR: 1.01; 95% CI: 1.00-1.02; P = .003), mean aortic valve gradient (OR: 1.03; 95% CI: 1.01-1.04; P < .001) and preserved LVEF (OR: 1.59; 95% CI: 1.02-2.48; P = .04), were associated with increased referral likelihood. Moreover, patients assessed by HVS referral as a time-dependent covariate had a significantly lower two-year mortality risk than those who were not (aHR: 0.30; 95% CI: 0.23-0.39; P < .001). CONCLUSION: A substantial proportion of severe AS patients meeting indications for AVR are not evaluated by HVS and experience markedly increased mortality. Further research is warranted to assess the efficacy of care delivery mechanisms, such as e-consults, and telemedicine, to improve access to HVS expertise.

An end-to-end multi-task system of automatic lesion detection and anatomical localization in whole-body bone scintigraphy by deep learning.

SUMMARY: Limited by spatial resolution and visual contrast, bone scintigraphy interpretation is susceptible to subjective factors, which considerably affects the accuracy and repeatability of lesion detection and anatomical localization. In this work, we design and implement an end-to-end multi-task deep learning model to perform automatic lesion detection and anatomical localization in whole-body bone scintigraphy. A total of 617 whole-body bone scintigraphy cases including anterior and posterior views were retrospectively analyzed. The proposed semi-supervised model consists of two task flows. The first one, the lesion segmentation flow, received image patches and was trained in a supervised way. The other one, skeleton segmentation flow, was trained on as few as five labeled images in conjunction with the multi-atlas approach, in a semi-supervised way. The two flows joint in their encoder layers so each flow can capture more generalized distribution of the sample space and extract more abstract deep features. The experimental results show that the architecture achieved the highest precision in the finest bone segmentation task in both anterior and posterior images of whole-body scintigraphy. Such an end-to-end approach with very few manual annotation requirement would be suitable for algorithm deployment. Moreover, the proposed approach reliably balances unsupervised labels construction and supervised learning, providing useful insight for weakly labeled image analysis. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Kinome and phosphoproteome reprogramming underlies the aberrant immune responses in critically ill COVID-19 patients.

SARS-CoV-2 infection triggers extensive host immune reactions, leading to severe diseases in certain individuals. However, the molecular basis underlying the excessive yet non-productive immune responses in severe COVID-19 remains incompletely understood. In this study, we conducted a comprehensive analysis of the peripheral blood mononuclear cell (PBMC) proteome and phosphoproteome in sepsis patients positive or negative for SARS-CoV-2 infection, as well as healthy subjects, using quantitative mass spectrometry. Our findings demonstrate dynamic changes in the COVID-19 PBMC proteome and phosphoproteome during disease progression, with distinctive protein or phosphoprotein signatures capable of distinguishing longitudinal disease states. Furthermore, SARS-CoV-2 infection induces a global reprogramming of the kinome and phosphoproteome, resulting in defective adaptive immune response mediated by the B and T lymphocytes, compromised innate immune responses involving the SIGLEC and SLAM family of immunoreceptors, and excessive cytokine-JAK-STAT signaling. In addition to uncovering host proteome and phosphoproteome aberrations caused by SARS-CoV-2, our work recapitulates several reported therapeutic targets for COVID-19 and identified numerous new candidates, including the kinases PKG1, CK2, ROCK1/2, GRK2, SYK, JAK2/3, TYK2, DNA-PK, PKCδ, and the cytokine IL-12.

Development of hypothyroidism following hemithyroidectomy: A population-based study.

PURPOSE: Hypothyroidism is a known possibility after hemithyroidectomy, with a highly variable incidence in the literature ranging from 8 to 60 %. Incidence of hypothyroidism after hemithyroidectomy was evaluated with a secondary aim to assess incidence in patients with Hashimoto's disease. MATERIALS & METHODS: A retrospective study using the TriNetX global federated research network was performed. We included patients within the last 15 years that were ≥18 years of age and had Current Procedural Terminology codes for hemithyroidectomy. Patients were excluded if they had a total or completion thyroidectomy at any time, a history of thyroid cancer, were preoperatively either on levothyroxine, diagnosed with hypothyroidism, or had a Thyroid Stimulating Hormone ≥ 4 m[IU]/L. We assessed the 3 month incidence of hypothyroidism postoperatively based on the International Classification of Diseases code, TSH ≥ 4 m[IU]/L, or taking levothyroxine after surgery. RESULTS: 6845 patients met the inclusion criteria. Most of the cohort was female (67 %) and white (63 %). The mean age at surgery for this population was 54 ± 14.8 years. During the 15 years of data, we found the 3-month incidence of hypothyroidism following hemithyroidectomy to be 23.58 %. The median time to develop the disease was 41.8 months. A subgroup analysis of those with Hashimoto's revealed a 3-month incidence of 31.1 % of patients developing hypothyroidism after surgery. CONCLUSIONS: This population-based study gives additional insight into the incidence of hypothyroidism after hemithyroidectomy. This will help improve perioperative patient counseling and management.

Prognostic significance of time trends in treatment of head and neck squamous cell carcinoma.

PURPOSE: To analyze the impact of demographic, clinical, and management variables on time to treatment initiation (TTI) and overall survival (OS). STUDY DESIGN: Retrospective chart review. MATERIALS AND METHODS: Medical records of patients diagnosed with head and neck cancer from 2018 to 2020 were reviewed. Univariate linear and Cox-regressions identified predictors of TTI and OS. Kaplan Meier (KM) curves assessed the difference in survival by diagnostic year and TTI. RESULTS: 381 patients met eligibility criteria. Median TTI was 35.0 days (IQR: 25.0-49.0). Only 10.8 % of all patients reported any treatment delay, with TTI exceeding 90 days found in 3.7 % of patients. TTI increased with African American race (p = 0.02), ED referrals (p = 0.02), and direct admission status (p = 0.01). When compared to treatment with surgery alone, TTI was shorter in patients undergoing surgery with adjuvant radiation (p = 0.02), adjuvant chemoradiation (p = 0.04), and salvage surgery (p = 0.04). Univariate Cox-regressions found smoking (p = 0.01), direct admission status (p = 0.02), increased duration of symptoms (p = 0.02), placement of PEG tubes (p < 0.01) and tracheostomies (p < 0.01), combination treatment (p < 0.01), and surgery with adjuvant chemoradiation treatment (p = 0.01) to increase mortality risk. Disease characteristics, including tumor size (p < 0.01), presence of nodal disease (p = 0.02), and late-stage disease (p < 0.01), increased mortality risk. TTI and diagnostic year did not impact survival. CONCLUSIONS: Our analysis determined several demographic, referral, and treatment factors impacted TTI. However, increased TTI did not impact survival. Characteristics consistent with advanced disease worsened OS. Despite the pandemic burden, patients diagnosed in 2020 showed no difference in short-term survival compared to prior years.

Dynamic interplay of two molecular switches enabled by the MEK1/2-ERK1/2 and IL-6-STAT3 signaling axes controls epithelial cell migration in response to growth factors.

Cell migration is an essential physiological process, and aberrant migration of epithelial cells underlies many pathological conditions. However, the molecular mechanisms governing cell migration are not fully understood. We report here that growth factor-induced epithelial cell migration is critically dependent on the crosstalk of two molecular switches, namely phosphorylation switch (P-switch) and transcriptional switch (T-switch). P-switch refers to dynamic interactions of deleted in liver cancer 1 (DLC1) and PI3K with tensin-3 (TNS3), phosphatase and tensin homolog (PTEN), C-terminal tension, and vav guanine nucleotide exchange factor 2 (VAV2) that are dictated by mitogen-activated protein kinase kinase 1/2-extracellular signal-regulated protein kinase 1/2-dependent phosphorylation of TNS3, PTEN, and VAV2. Phosphorylation of TNS3 and PTEN on specific Thr residues led to the switch of DLC1-TNS3 and PI3K-PTEN complexes to DLC1-PTEN and PI3K-TNS3 complexes, whereas Ser phosphorylation of VAV2 promotes the transition of the PI3K-TNS3/PTEN complexes to PI3K-VAV2 complex. T-switch denotes an increase in C-terminal tension transcription/expression regulated by both extracellular signal-regulated protein kinase 1/2 and signal transducer and activator of transcription 3 (STAT3) via interleukin-6-Janus kinase-STAT3 signaling pathway. We have found that, the P-switch is indispensable for both the initiation and continuation of cell migration induced by growth factors, whereas the T-switch is only required to sustain cell migration. The interplay of the two switches facilitated by the interleukin-6-Janus kinase-STAT3 pathway governs a sequence of dynamic protein-protein interactions for sustained cell migration. That a similar mechanism is employed by both normal and tumorigenic epithelial cells to drive their respective migration suggests that the P-switch and T-switch are general regulators of epithelial cell migration and potential therapeutic targets.

Generic Plug-and-Play Strategy for High-Throughput Analysis of PTM-Mediated Protein Complexes.

Protein complexes mediated by various post-translational modifications (PTMs) play important roles in almost every aspect of biological processes. PTM-mediated protein complexes often have weak and transient binding properties, which limit their unbiased profiling especially in complex biological samples. Here, we developed a plug-and-play chemical proteomic approach for high-throughput analyis of PTM-mediated protein complexes. Taking advantage of the glutathione-S-transferase (GST) tag, which is the gold standard for protein purification and has wide access to a variety of proteins of interest (POIs), a glutathione (GSH) group- and photo-cross-linking group-containing trifunctional chemical probe was developed to tag POIs and assembled onto a streptavidin-coated 96-well plate for affinity purification, photo-cross-linking, and proteomics sample preparation in a fully integrated manner. Compared with the previously developed photo-pTyr-scaffold strategy, by assembling the tyrosine phosphorylation (pTyr) binding domain through covalent NHS chemistry, the new plug-and-play strategy using a noncovalent GST-GSH interaction has comparable enrichment efficiency for EGF stimulation-dependent pTyr protein complexes. To further prove its feasibility, we additionally assembled four pTyr-binding domains in the 96-well plate and selectively identified their pTyr-dependent interacting proteins. Importantly, we systematically optimized and applied the plug-and-play approach for exploring protein methylation-mediated protein complexes, which are difficult to be characterized due to their weak binding affinity and the lack of efficient enrichment strategies. We explored a comprehensive protein methylation-mediated interaction network assembled by five protein methylation binding domains including the chromo domain of MPP8, tandem tudor domain of KDM4A, full-length CBX1, PHD domain of RAG2, and tandem tudor domain of TP53BP1 and validated the chromo domain- and tudor domain-mediated interaction with histone H3. Collectively, this plug-and-play approach provides a convenient and generic strategy for exploring PTM-dependent protein complexes for any POIs with the GST tag.

Incidence of synchronous malignancies found during triple endoscopy in head and neck cancer.

OBJECTIVES: To investigate the incidence of synchronous malignancies identified during triple endoscopy in patients with head and neck squamous cell carcinoma. METHODS: A retrospective chart review of patients from a tertiary academic medical center was performed. Patients with a primary head and neck squamous cell carcinoma who underwent triple endoscopy were included. Operative, radiographic, and pathology reports were reviewed to evaluate for the presence of synchronous malignancies in the aerodigestive tract diagnosed through endoscopy. Demographics, relevant medical history, including tobacco and alcohol use, and tumor characteristics were recorded. Univariate and multivariate regression analyses were conducted to assess for associations with synchronous malignancy on triple endoscopy. RESULTS: 215 patients were reviewed, 164 of which had a biopsy-positive head and neck squamous cell carcinoma and underwent triple endoscopy. Synchronous lesions were found in 8 patients (4.9%). Of the synchronous lesions, only two were identified on esophagoscopy and bronchoscopy; the remaining six were found on direct laryngoscopy. Clinical comorbidities including smoking and alcohol history, tumor p16 status, and tumor stage were not associated with presence of synchronous lesions. A positive synchronous lesion on positron emission tomography was significantly correlated with finding a synchronous lesion on triple endoscopy (p = 0.006). CONCLUSION: This study shows the incidence of synchronous lesions on triple endoscopy to be closer to 5%. While endoscopic examination can be useful in the anatomic characterization of head and neck malignancies, the low incidence of synchronous malignancies suggests that the need for triple endoscopy may be considered on a case-by-case basis.

The impact of microscopic versus macroscopic extranodal extension in oral cavity squamous cell carcinoma: National cancer database analysis and review of the literature.

OBJECTIVE: To analyze the prognostic significance of microscopic vs macroscopic extranodal extension and to assess the impact of chemoradiation on overall survival among patients with oral cavity squamous cell carcinoma and varying degrees of extranodal extension. METHODS: Utilizing the National Cancer Database, we performed a retrospective cohort study of 7975 patients with oral cavity squamous cell carcinoma and varying degrees of extranodal extension who underwent primary surgical intervention. Propensity-score matched models following Cox regression analyses allowed us to assess the impact of adjuvant radiation alone vs adjuvant chemoradiation on overall survival in patients with microscopic extranodal extension and macroscopic extranodal extension. RESULTS: 7975 patients with oral cavity squamous cell carcinoma were included in the final analysis. Within this cohort, 25.4% had microscopic extranodal extension and 5.2% had macroscopic extranodal extension. On univariate analysis, we found that microscopic and macroscopic extranodal extension were associated with decreased overall survival when compared to those with positive nodes without extranodal extension (HR = 1.67; 95% CI 1.56, 1.79 and HR = 1.88; 95% CI 1.66, 2.14, respectively). On multivariate analysis after propensity-score matching, we found no significant difference in overall survival in patients who received adjuvant radiation alone vs. adjuvant chemoradiation for both microscopic and macroscopic extranodal extension. CONCLUSION: Our data suggest that microscopic extranodal extension in oral cavity squamous cell carcinoma is associated with worse overall survival than patients without extranodal extension following primary surgical intervention with neck dissection. The results of this study also suggest that the addition of chemotherapy to adjuvant radiation may not provide a significant survival benefit in patients with oral cavity squamous cell carcinoma with microscopic and macroscopic extranodal extension. Comprehensive assessment of the benefits of adjuvant chemoradiation in the setting of microscopic vs macroscopic extranodal extension would need to be studied in a randomized controlled trial.

Impact of intraoperative ischemia time on acute complications of head and neck microvascular free tissue transfer: A systematic review and meta-analysis.

BACKGROUND: To evaluate the relationship between intraoperative ischemia time with acute microvascular free tissue transfer (MFTT) complications in head and neck reconstruction. METHODS: A systematic review using PRISMA guidelines was performed. Inclusion encompassed all available studies published and indexed using PubMed, Medline, and Embase. Meta-analyses were performed using the Cochrane Review Manager tool. Methodological Index for Non-Randomized Studies (MINORS), the Revised Cochrane risk-of-bias tool for randomized trials, and the NIH Study Quality Assessment Tool for non-randomized prospective studies. RESULTS: A total of 430 citations were reviewed. 25 were included in our overall qualitative analysis, and 14 for meta-analysis. When comparing ischemia times for flaps with and without complications, no significant difference was observed (p = 0.98). Additionally, in a separate cohort, no significant effect was realized when correlating ischemia time to overall rates and total complications. CONCLUSION: Ischemia time was not significantly different between those with and without acute flap complications.

Job market in head and neck surgery: A survey and analysis of recent fellowship graduates.

OBJECTIVE: Recent years have seen increase in individuals pursuing postgraduate fellowships in head and neck (HN) surgery. This has presented concerns about insufficient jobs where graduates can apply their scope of specialized training. METHODS: Data was collected in two manners- a survey and a manual online search of American Head and Neck Society (AHNS) fellowship graduates. A 25-question survey was sent in 2021 to approximately 400 HN fellows who graduated between 2010 and 2020. The AHNS list of graduates from the same years were searched online to collect information including gender, graduation year, fellowship training, and current job practice. RESULTS: Of the 78 survey responses, 64.1 % were male and 34.6 % female. 96.2 % reported ablative, 84.6 % microvascular, and 82.1 % TORS training. Mean number of interviews was 4 with most interviewing during the 3rd quarter (January to March). Majority reported being in academic and university-based practices (79.6 %). Online search was done on 393 graduates. Since 2010 the number of graduates almost doubled. There was a statistically significant increase in females by year (p = 0.022). There was a significant decrease (p = 0.022) in graduates with additional fellowship training from that of their AHNS fellowship. There was also a statistically significant increase in graduates being in academic practices (p = 0.022). CONCLUSION: Despite growing numbers, there appears to be more graduates entering an academic practice, although the definition of an academic HN practice may be evolving. These results provide guidance on how to approach the job search in a select market. LEVEL OF EVIDENCE: II.

DLC1 SAM domain-binding peptides inhibit cancer cell growth and migration by inactivating RhoA.

Deleted-in-liver cancer 1 (DLC1) exerts its tumor suppressive function mainly through the Rho-GTPase-activating protein (RhoGAP) domain. When activated, the domain promotes the hydrolysis of RhoA-GTP, leading to reduced cell migration. DLC1 is kept in an inactive state by an intramolecular interaction between its RhoGAP domain and the DLC1 sterile α motif (SAM) domain. We have shown previously that this autoinhibited state of DLC1 may be alleviated by tensin-3 (TNS3) or PTEN. We show here that the TNS3/PTEN-DLC1 interactions are mediated by the C2 domains of the former and the SAM domain of the latter. Intriguingly, the DLC1 SAM domain was capable of binding to specific peptide motifs within the C2 domains. Indeed, peptides containing the binding motifs were highly effective in blocking the C2-SAM domain-domain interaction. Importantly, when fused to the tat protein-transduction sequence and subsequently introduced into cells, the C2 peptides potently promoted the RhoGAP function in DLC1, leading to decreased RhoA activation and reduced tumor cell growth in soft agar and migration in response to growth factor stimulation. To facilitate the development of the C2 peptides as potential therapeutic agents, we created a cyclic version of the TNS3 C2 domain-derived peptide and showed that this peptide readily entered the MDA-MB-231 breast cancer cells and effectively inhibited their migration. Our work shows, for the first time, that the SAM domain is a peptide-binding module and establishes the framework on which to explore DLC1 SAM domain-binding peptides as potential therapeutic agents for cancer treatment.

Phosphorylation-dependent substrate selectivity of protein kinase B (AKT1).

Protein kinase B (AKT1) is a central node in a signaling pathway that regulates cell survival. The diverse pathways regulated by AKT1 are communicated in the cell via the phosphorylation of perhaps more than 100 cellular substrates. AKT1 is itself activated by phosphorylation at Thr-308 and Ser-473. Despite the fact that these phosphorylation sites are biomarkers for cancers and tumor biology, their individual roles in shaping AKT1 substrate selectivity are unknown. We recently developed a method to produce AKT1 with programmed phosphorylation at either or both of its key regulatory sites. Here, we used both defined and randomized peptide libraries to map the substrate selectivity of site-specific, singly and doubly phosphorylated AKT1 variants. To globally quantitate AKT1 substrate preferences, we synthesized three AKT1 substrate peptide libraries: one based on 84 "known" substrates and two independent and larger oriented peptide array libraries (OPALs) of ∼1011 peptides each. We found that each phospho-form of AKT1 has common and distinct substrate requirements. Compared with pAKT1T308, the addition of Ser-473 phosphorylation increased AKT1 activities on some, but not all of its substrates. This is the first report that Ser-473 phosphorylation can positively or negatively regulate kinase activity in a substrate-dependent fashion. Bioinformatics analysis indicated that the OPAL-activity data effectively discriminate known AKT1 substrates from closely related kinase substrates. Our results also enabled predictions of novel AKT1 substrates that suggest new and expanded roles for AKT1 signaling in regulating cellular processes.