Immunosensitivity mediated by downregulated AKT1-SKP2 induces anti-PD-1-associated thyroid immune injury.

BACKGROUND: Immune checkpoint inhibitors evoke the immune system, which may cause immune-related adverse effects. The predictors and mechanisms of anti-PD-1-associated thyroid immune injury remain unclear. METHODS: A retrospective analysis is conducted on 518 patients treated with anti PD-1/PD-L1. Firstly, the differences between anti PD-1 and anti PD-L1 are compared on the risk of thyroid immune injury. Then, the predictors of the risk and thyroid function for anti PD-1 related thyroid immune injury are analyzed. Furthermore, the in vitro mechanism of normal thyroid cells (NTHY) is studied. First, the effect of anti PD-1 on the cell viability and immune sensitivity of thyroid cells is observed. Cell viability includes cell proliferation, apoptosis, cell cycle, T4 secretion, while immune sensitivity includes molecular expression and CD8 + T cell aggregation and killing towards NTHY. Then the differentially expressed proteins (DEPs) are screened by protein mass spectrometry. Enrichment of KEGG pathway and annotation of GO function on DEPs are conducted. Human protein-protein interactions are obtained from STRING database. The network is constructed and analyzed using Cytoscape software. In vitro, key proteins and their pathways are validated through overexpression plasmids or inhibitors. The recovery experiment and the immuno-coprecipitation experiment are designed to support the results. In vivo, the key proteins are detected in the thyroid tissue of mice fed with anti PD-1, as well as in the thyroid tissue of patients with Hashimoto's thyroiditis. RESULTS: Thyroid irAE is associated with female, IgG, FT4, TPOAb, TGAb, TSHI, TFQI, and TSH. Peripheral lymphocytes are associated with thyroid function. In vitro, the NIVO group shows prologed G1 phase, decreased FT4, downregulated PD-L1, upregulated IFN-γ, and more CD8 + T cell infiltration and cytotoxicity. AKT1-SKP2 is chosen as the key protein. AKT1 overexpression and SKP2 inhibitor replies to NIVO and AKT1 overexpression, respectively. Immunoprecipitation shows SKP2 and PD-L1 interaction. CONCLUSION: Female, impaired thyroid hormone sensitivity and IgG4 contribute to the risk of thyroid irAE, while peripheral blood lymphocyte characteristics affect thyroid function. Anti-PD-1 induces thyroid irAE by downregulating AKT1-SKP2 to enhance thyroid immunosensitivity.

Screening of antitumor polypeptide drug and enhanced CT imaging based on drug target analysis.

Molecular targeted antitumor drugs is a major progress in recent years, these drugs usually target specific molecules to tumor cell signaling pathways, reduce toxicity, and can achieve individualized treatment. In this study, we screened three polypeptide proteins by yeast two hybrid systems, which could inhibit tumor growth obviously. The results of this study are expected to further develop new antitumor drugs. Moreover, by using contrast-enhanced computed tomography (CECT) imaging, this study proposes an algorithm for the computer-aided diagnosis (CAD) and classification of adrenal tumors. The experimental results demonstrate an excellent classification performance of this algorithm. Therefore, the method proposed in this paper may accurately locate and qualitatively diagnose the adrenal tumor in an effective manner, thereby providing important references for treatment.

Proliferation unleashed: the role of Skp2 in vascular smooth muscle cell proliferation.

Vascular smooth muscle cell proliferation plays a major role in the development of numerous vascular pathologies. Understanding the molecular mechanisms that regulate smooth muscle cell proliferation is therefore essential for the development of new therapies for the treatment of these pathologies. Skp2 is an F-box protein component of the SCFSkp2 ubiquitin-ligase that controls cellular proliferation by regulating the ubiquitination and degradation of several cell-cycle regulatory proteins, including the cyclin-dependent kinase inhibitor, p27Kip1. This review discusses the recent literature on the function and regulation of Skp2 in smooth muscle cells, which is emerging as a key player in the control of smooth muscle cell proliferation during vascular disease.

Skp2 enhances polyubiquitination and degradation of TIS21/BTG2/PC3, tumor suppressor protein, at the downstream of FoxM1.

TIS21(/BTG2/PC3) has been shown to work as a pan-cell cycle inhibitor and a negative regulator of cyclin B1/cdk1 and forkhead box M1 (FoxM1). Moreover, loss of TIS21 expression has been suggested as an early event in carcinogenesis of thymus, prostate, kidney, and liver. However, there is no report yet what regulates the in vivo stability of TIS21 protein. Here, TIS21 was found to be a target of ubiquitin ligase, S phase kinase associated protein 2 (Skp2), the expression of which was regulated by FoxM1. Leucine rich repeat (LRR) domain of Skp2 could bind to TIS21 C-terminus and facilitated TIS21 degradation via ubiquitin-proteasome pathway. Skp2 without LRR and C-terminus deleted TIS21 (TIS21DeltaC) failed to interact with each other, and failure of their interaction prolonged half-life of TIS21 protein. Furthermore, in vivo function of TIS21, inhibition of cell growth, was regulated by expressions of Skp2 and FoxM1; It was significantly enhanced by knock down of Skp2 expression in the TIS21 adenovirus infected cells, whereas it was significantly ameliorated by co-expression of FoxM1 with TIS21. These data indicate that TIS21 is a novel target of SCF-Skp2 ubiquitin ligase, which is regulated by expression of FoxM1.

ERK activity and G1 phase progression: identifying dispensable versus essential activities and primary versus secondary targets.

The ERK subfamily of MAP kinases is a critical regulator of S phase entry. ERK activity regulates the induction of cyclin D1, and a sustained ERK signal is thought to be required for this effect, at least in fibroblasts. We now show that early G1 phase ERK activity is dispensable for the induction of cyclin D1 and that the critical ERK signaling period is restricted to 3-6 h after mitogenic stimulation of quiescent fibroblasts. Similarly, early G1 phase ERK activity is dispensable for entry into S phase. Moreover, if cyclin D1 is expressed ectopically, ERK activity becomes dispensable throughout the G1 phase. In addition to its effect on cyclin D1, ERK activity is thought to contribute to the down-regulation of p27kip1. We found that this effect is restricted to late G1/S phase. Mechanistic analysis showed that the ERK effect on p27kip1 is mediated by Skp2 and is secondary to its effect on cyclin D1. Our results emphasize the importance of mid-G1 phase ERK activity and resolve primary versus secondary ERK targets within the G1 phase cyclin-dependent kinases.

Knockdown of Skp2 by siRNA inhibits melanoma cell growth in vitro and in vivo.

BACKGROUND: Low levels of p27Kip1 expression are associated with poor prognosis in various malignancies including malignant melanoma. Recently, it has been reported that S phase kinase-interacting protein 2 (Skp2), the specific ubiquitin ligase subunit that targets p27Kip1 for degradation, was overexpressed and was inversely related to p27Kip1 levels in malignant melanoma with poor prognosis. OBJECTIVE: We investigated whether small interfering RNA (siRNA)-mediated gene silencing of Skp2 can be employed in order to inhibit p27Kip1 down-regulation and suppress melanoma cell growth as a consequence in vitro and in vivo. METHODS: We constructed a plasmid vector, which synthesizes siRNAs to determine the effects of decreasing the high constitutive levels of Skp2 protein in melanoma cells. Western blot and real-time RT-PCR were performed to examine the decreases of Skp2 protein and mRNA in vitro. Furthermore, melanoma cells were injected into the back of nude mice subcutaneously to examine the suppression of tumorigenicity targeting Skp2 gene silencing in vivo. RESULTS: Skp2 protein was decreased and the p27Kip1 protein was accumulated in Skp2 siRNA transfected melanoma cells. Skp2 siRNA inhibited the cell growth of melanoma cells in vitro. Moreover, Skp2 siRNA also suppressed tumor proliferation in vivo. CONCLUSION: Our results suggest that siRNA-mediated gene silencing of Skp2 can be a potent tool of cancer gene therapy for suppression of p27Kip1 degradation in malignant melanoma.

p27/Kip1 mediates retinoic acid-induced suppression of ovarian carcinoma cell growth.

We have investigated the mechanisms by which all-trans retinoic acid (ATRA) causes growth inhibition of ovarian carcinoma cells. As a model, we have studied the CAOV3 cell line, which is sensitive to ATRA, and the SKOV3 cell line, which is resistant. We have found that treatment of CAOV3 cells with ATRA causes a 5-10 fold increase in the protein level of the cyclin dependent kinase inhibitor p27/Kip1. p27/Kip1 protein upregulation is important in ovarian carcinoma as primary tumors are frequently found lacking this protein. The increase in p27/Kip1 is detected by day 3 of ATRA treatment of CAOV3 cells, and is maximal by day 5. Messenger RNA levels of p27/Kip1 do not change in CAOV3 cells following ATRA treatment, however, we have shown that p27/Kip1 mRNA is more stable in ATRA treated CAOV3 cells. Conversely, the ATRA resistant cell line SKOV3 fails to show p27/Kip1 accumulation. Interestingly, the SCF component protein SKP2 appears to be decreased in CAOV3 cells treated with ATRA. We have also shown that the ATRA dependent increase in p27/kip1 protein in CAOV3 cells leads to a decrease in the kinase activity of cyclin dependent kinase 4 (CDK4) following ATRA treatment. Finally, we found that CAOV3 cells stably transfected with a p27/kip1antisense construct, which express lower levels of p27/kip1 following ATRA treatment, and have a higher CDK4 kinase activity are less sensitive to ATRA induced growth suppression. Taken together our data suggest ATRA-induced growth inhibition in CAOV3 ovarian carcinoma cells involves modulation of the CDK inhibitor p27/kip1.

Negative regulation of SCFSkp2 ubiquitin ligase by TGF-beta signaling.

TGF-beta is a multifunctional growth factor whose best-known function is to inhibit cell growth and suppress tumor formation. TGF-beta causes cells to accumulate in mid-to-late G1 phase by blocking the transition from G1 to S. It has been shown that TGF-beta inhibits Cdk2-cyclin E kinase activity by promoting the binding of cell cycle inhibitor p27Kip1 to the kinase complexes. Here, we show that TGF-beta treatment leads to stabilization of p27Kip1 during G1 to S transition. We found that TGF-beta negatively regulates components of the SCF complex, which degrades the p27Kip1 during the G1 to S transition, through two distinct mechanisms. Using a pulse-chase analysis, we demonstrated that the stability of Skp2 decreases in the presence of TGF-beta. Destabilization of Skp2 by ubiquitin-mediated proteolysis was also demonstrated that in an in vitro degradation system, using cell extracts prepared from TGF-beta-treated cultured cells. In addition, TGF-beta treatment decreases the levels of Cks1 mRNA. The deficiency of Cks1 in TGF-beta-treated cells likely contributes to the stabilization of p27Kip1 and destabilization of Skp2, because in the absence of Cks1, SCFSkp2 cannot ubiquitinate p27Kip1; instead, self-ubiquitination of Skp2 occurs. Thus, stabilization of the cell cycle inhibitor p27Kip1 and cell growth inhibition in response to TGF-beta occur in part through limiting the threshold of the SCFSkp2 ubiquitin ligase by transcriptional and post-transcriptional mechanisms.

Retinoic acid decreases targeting of p27 for degradation via an N-myc-dependent decrease in p27 phosphorylation and an N-myc-independent decrease in Skp2.

Poor prognosis neuroblastoma (NB) tumors are marked by amplification and overexpression of N-myc. Retinoic acid (RA) decreases N-myc levels and induces cell cycle arrest in vitro and increases event-free survival in advanced stage NB patients. In this study, we investigated the mechanism(s) by which RA regulates cell cycle and how N-myc affects NB cell cycle progression. Constitutive N-myc overexpression stimulates increases in cyclin E-dependent kinase activity and decreases in p27 resulting in increased DNA synthesis. N-myc regulates p27 levels through an increase in targeting of p27 to the proteasome via cyclin E kinase-dependent phosphorylation of p27 and its ubiquitination. N-myc also stimulates an increase in proteasome activity. In RA-treated cells in which N-myc levels decline as p27 levels increase, degradation of p27 is also decreased. However, RA does not affect the activity of proteasome. The decrease in the degradation of p27 in RA-treated cells is due in part to a decrease in the N-myc stimulated phosphorylation of p27. However, RA also decreases Skp2 levels thus impairing the ability of p27 to be ubiquitinated. Thus, RA induces both N-myc-dependent and -independent mechanisms to minimize the degradation of p27 and arrest NB cell growth.