Cyclin D3 expression in melanoma cells is regulated by adhesion-dependent phosphatidylinositol 3-kinase signaling and contributes to G1-S progression

Role of serine 365 in BRAF V600E sensitivity to RAF inhibition

The serine-threonine kinase, BRAF, is an upstream regulator of the MEK-ERK1/2 pathway and is commonly mutated in cancer. 14-3-3 proteins bind to two sites in BRAF, N-terminal S365, and C-terminal S729. 14-3-3 binding modulates the activity and dimerization of both wild-type and non-V600 mutant forms of BRAF. In BRAF V600E mutants, the C-terminal S729 site affects dimerization of truncated splice variants. The N-terminal, S365, is removed in BRAF V600E splice variants but its importance in full-length BRAF V600 mutants remains uncertain. We tested the role of S365 in dimerization and RAF inhibitor resistance in full-length BRAF V600E. Mutating BRAF S365 site to an alanine (S365A) reduced 14-3-3 association and increased BRAF V600E homodimerization. BRAF V600E S365A displayed reduced sensitivity to RAF inhibitor at the level of MEK-ERK1/2 signaling, cell growth, and cell viability. These data suggest that alteration or removal of the S365 14-3-3 binding site may contribute to RAF inhibitor resistance.

Selective inhibition of Ph-positive ALL cell growth through kinase-dependent and -independent effects by CDK6-specific PROTACs

Expression of the cell cycle regulatory gene CDK6 is required for Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL) cell growth, whereas expression of the closely related CDK4 protein is dispensable. Moreover, CDK6 silencing is more effective than treatment with the dual CDK4/6 inhibitor palbociclib in suppressing Ph+ ALL in mice, suggesting that the growth-promoting effects of CDK6 are, in part, kinase-independent in Ph+ ALL. Accordingly, we developed CDK4/6-targeted proteolysis-targeting chimeras (PROTACs) that inhibit CDK6 enzymatic activity in vitro, promote the rapid and preferential degradation of CDK6 over CDK4 in Ph+ ALL cells, and markedly suppress S-phase cells concomitant with inhibition of CDK6-regulated phospho-RB and FOXM1 expression. No such effects were observed in CD34+ normal hematopoietic progenitors, although CDK6 was efficiently degraded. Treatment with the CDK6-degrading PROTAC YX-2-107 markedly suppressed leukemia burden in mice injected with de novo or tyrosine kinase inhibitor-resistant primary Ph+ ALL cells, and this effect was comparable or superior to that of the CDK4/6 enzymatic inhibitor palbociclib. These studies provide "proof of principle" that targeting CDK6 with PROTACs that inhibit its enzymatic activity and promote its degradation represents an effective strategy to exploit the "CDK6 dependence" of Ph+ ALL and, perhaps, of other hematologic malignancies. Moreover, they suggest that treatment of Ph+ ALL with CDK6-selective PROTACs would spare a high proportion of normal hematopoietic progenitors, preventing the neutropenia induced by treatment with dual CDK4/6 inhibitors.

BRAF Splice Variant Resistance to RAF Inhibitor Requires Enhanced MEK Association

Expression of aberrantly spliced BRAF V600E isoforms (BRAF V600E ΔEx) mediates resistance in 13%-30% of melanoma patients progressing on RAF inhibitors. BRAF V600E ΔEx confers resistance, in part, through enhanced dimerization. Here, we uncoupled BRAF V600E ΔEx dimerization from maintenance of MEK-ERK1/2 signaling. Furthermore, we show BRAF V600E ΔEx association with its substrate, MEK, is enhanced and required for RAF inhibitor resistance. RAF inhibitor treatment increased phosphorylation at serine 729 (S729) in BRAF V600E ΔEx. Mutation of S729 to a non-phosphorylatable residue reduced BRAF V600E ΔEx-MEK interaction, reduced dimerization or oligomerization, and increased RAF inhibitor sensitivity. Conversely, mutation of the BRAF dimerization domain elicited partial effects on MEK association and RAF inhibitor sensitivity. Our data implicate BRAF S729 in resistance to RAF inhibitor and underscore the importance of substrate association with BRAF V600E ΔEx. These findings may provide opportunities to target resistance driven by aberrantly spliced forms of BRAF V600E.

In Vivo ERK1/2 Reporter Predictively Models Response and Resistance to Combined BRAF and MEK Inhibitors in Melanoma

Combined BRAF and MEK inhibition is a standard of care in patients with advanced BRAF-mutant melanoma, but acquired resistance remains a challenge that limits response durability. Here, we quantitated in vivo ERK1/2 activity and tumor response associated with resistance to combined BRAF and MEK inhibition in mutant BRAF xenografts. We found that ERK1/2 pathway reactivation preceded the growth of resistant tumors. Moreover, we detected a subset of cells that not only persisted throughout long-term treatment but restored ERK1/2 signaling and grew upon drug removal. Cell lines derived from combination-resistant tumors (CRT) exhibited elevated ERK1/2 phosphorylation, which were sensitive to ERK1/2 inhibition. In some CRTs, we detected a tandem duplication of the BRAF kinase domain. Monitoring ERK1/2 activity in vivo was efficacious in predicting tumor response during intermittent treatment. We observed maintained expression of the mitotic regulator, polo-like kinase 1 (Plk1), in melanoma resistant to BRAF and MEK inhibitors. Plk1 inhibition induced apoptosis in CRTs, leading to slowed growth of BRAF and MEK inhibitor-resistant tumors in vivo These data demonstrate the utility of in vivo ERK1/2 pathway reporting as a tool to optimize clinical dosing schemes and establish suppression of Plk1 as potential salvage therapy for BRAF inhibitor and MEK inhibitor-resistant melanoma.

Targeting FER Kinase Inhibits Melanoma Growth and Metastasis

Melanoma is one of the most aggressive types of tumors and exhibits high metastatic potential. Fes-related (FER) kinase is a non-receptor tyrosine kinase that has been implicated in growth and metastasis of various epithelial tumors. In this study, we have examined the role that FER kinase plays in melanoma at the molecular level. FER-depleted melanoma cells exhibit impaired Wnt/β-catenin pathway activity, as well as multiple proteomic changes, which include decreased abundance of L1-cell adhesion molecule (L1-CAM). Consistent with the pro-metastatic functions of these pathways, we demonstrate that depletion of FER kinase decreases melanoma growth and formation of distant metastases in a xenograft model. These findings indicate that FER is an important positive regulator of melanoma metastasis and a potential target for innovative therapies.

Targeting CDK6 and BCL2 Exploits the "MYB Addiction" of Ph+ Acute Lymphoblastic Leukemia

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ ALL) is currently treated with BCR-ABL1 tyrosine kinase inhibitors (TKI) in combination with chemotherapy. However, most patients develop resistance to TKI through BCR-ABL1-dependent and -independent mechanisms. Newly developed TKI can target Ph⁺ ALL cells with BCR-ABL1-dependent resistance; however, overcoming BCR-ABL1-independent mechanisms of resistance remains challenging because transcription factors, which are difficult to inhibit, are often involved. We show here that (i) the growth of Ph⁺ ALL cell lines and primary cells is highly dependent on MYB-mediated transcriptional upregulation of CDK6, cyclin D3, and BCL2, and (ii) restoring their expression in MYB-silenced Ph⁺ ALL cells rescues their impaired proliferation and survival. Levels of MYB and CDK6 were highly correlated in adult Ph⁺ ALL (P = 0.00008). Moreover, Ph⁺ ALL cells exhibited a specific requirement for CDK6 but not CDK4 expression, most likely because, in these cells, CDK6 was predominantly localized in the nucleus, whereas CDK4 was almost exclusively cytoplasmic. Consistent with their essential role in Ph⁺ ALL, pharmacologic inhibition of CDK6 and BCL2 markedly suppressed proliferation, colony formation, and survival of Ph⁺ ALL cells ex vivo and in mice. In summary, these findings provide a proof-of-principle, rational strategy to target the MYB "addiction" of Ph⁺ ALL.Significance: MYB blockade can suppress Philadelphia chromosome-positive leukemia in mice, suggesting that this therapeutic strategy may be useful in patients who develop resistance to imatinib and other TKIs used to treat this disease. Cancer Res; 78(4); 1097-109. ©2017 AACR.

Treatment of melanoma with selected inhibitors of signaling kinases effectively reduces proliferation and induces expression of cell cycle inhibitors

Cancer treatment often tends to involve direct targeting enzymes essential for the growth and proliferation of cancer cells. The aim of this study was the recognition of the possible role of selected protein kinases: PI3K, ERK1/2, and mTOR in cell proliferation and cell cycle in malignant melanoma. We investigated the role of protein kinase inhibitors: U0126 (ERK1/2), LY294002 (PI3K), rapamycin (mTOR), everolimus (mTOR), GDC-0879 (B-RAF), and CHIR-99021 (GSK3beta) in cell proliferation and expression of crucial regulatory cell cycle proteins in human melanoma cells: WM793 (VGP) and Lu1205 (metastatic). They were used either individually or in various combinations. The study on the effect of signaling kinases inhibitors on proliferation—BrdU ELISA test after 48–72 h. Their effect on the expression of cell cycle regulatory proteins: cyclin D1 and D3, cyclin-dependent kinase CDK4 and CDK6, and cell cycle inhibitors: p16, p21, and p27, was studied at the protein level (western blot). Treatment of melanoma cells with protein kinase inhibitors led to significantly decreased cell proliferation except the use of a GSK-3β kinase inhibitors—CHIR-99021. The significant decrease in the expression of selected cyclins and cyclin-dependent kinases (CDKs) with parallel increase in the expression of some of cyclin-dependent kinases inhibitors and in consequence meaningful reduction in melanoma cell proliferation by the combinations of inhibitors of signaling kinases clearly showed the crucial role of AKT, ERK 1/2, and mTOR signal transduction in melanoma progression. The results unanimously indicate those pathways as an important target for treatment of melanoma.

Role of cyclins D1 and D3 in vestibular schwannoma

BACKGROUND

Vestibular schwannomas in younger patients have been observed to be larger in size and grow more quickly.

OBJECTIVE

This study aimed to evaluate the expression of three important cell cycle proteins, cyclin D1, cyclin D3 and Ki-67, in vestibular schwannoma patients separated into two age groups: ≤ 40 years or > 40 years.

METHOD

Immunohistochemical detection of cyclin D1, cyclin D3 and Ki-67 was undertaken in 180 surgically resected vestibular schwannomas.

RESULTS

The proliferation index of vestibular schwannomas was statistically higher in the ≤ 40 years age group compared to that in the > 40 years age group (mean of 4.52 vs 3.27, respectively; p = 0.01). Overexpression of cyclin D1 and cyclin D3 was found in 68 per cent and 44 per cent of tumours, respectively.

CONCLUSION

There was an increased Ki-67 proliferation index in the younger age group that appears to correlate with clinical behaviour. Vestibular schwannomas in both age groups show increased expression of cyclin D1 and cyclin D3.

Combination of pan-RAF and MEK inhibitors in NRAS mutant melanoma

BACKGROUND

Approximately 20% of melanomas contain a mutation in NRAS. However no direct inhibitor of NRAS is available. One of the main signaling pathways downstream of NRAS is the MAPK pathway. In this study we investigated the possibility of blocking oncogenic signaling of NRAS by inhibiting two signaling points in the MAPK pathway.

METHODS

Fourteen NRAS mutated human melanoma cell lines were treated with a pan-RAF inhibitor (PRi, Amgen Compd A), a MEK inhibitor (MEKi, trametinib) or their combination and the effects on proliferation, cell cycle progression, apoptosis, transcription profile and signaling of the cells were investigated.

RESULTS

The majority of the cell lines showed a significant growth inhibition, with high levels of synergism of the PRi and MEKi combination. Sensitive cell lines showed induction of apoptosis by the combination treatment and there was a correlation between p-MEK levels and synergistic effect of the combination treatment. Proliferation of sensitive cell lines was blocked by the inhibition of the MAPK pathway, which also blocked expression of cyclin D1. However, in resistant cell lines, proliferation was blocked by combined inhibition of the MAPK pathway and cyclin D3, which is not regulated by the MAPK pathway. Resistant cell lines also showed higher levels of p-GSK3β and less perturbation of the apoptotic profile upon the treatment in comparison with the sensitive cell lines.

CONCLUSIONS

The combination of PRi + MEKi can be an effective regimen for blocking proliferation of NRAS mutant melanomas when there is higher activity of the MAPK pathway and dependence of proliferation and survival on this pathway.

The history and future of targeting cyclin-dependent kinases in cancer therapy

Cancer represents a pathological manifestation of uncontrolled cell division; therefore, it has long been anticipated that our understanding of the basic principles of cell cycle control would result in effective cancer therapies. In particular, cyclin-dependent kinases (CDKs) that promote transition through the cell cycle were expected to be key therapeutic targets because many tumorigenic events ultimately drive proliferation by impinging on CDK4 or CDK6 complexes in the G1 phase of the cell cycle. Moreover, perturbations in chromosomal stability and aspects of S phase and G2/M control mediated by CDK2 and CDK1 are pivotal tumorigenic events. Translating this knowledge into successful clinical development of CDK inhibitors has historically been challenging, and numerous CDK inhibitors have demonstrated disappointing results in clinical trials. Here, we review the biology of CDKs, the rationale for therapeutically targeting discrete kinase complexes and historical clinical results of CDK inhibitors. We also discuss how CDK inhibitors with high selectivity (particularly for both CDK4 and CDK6), in combination with patient stratification, have resulted in more substantial clinical activity.

In vivo MAPK reporting reveals the heterogeneity in tumoral selection of resistance to RAF inhibitors

Activation of the ERK1/2 mitogen-activated protein kinases (MAPK) confers resistance to the RAF inhibitors vemurafenib and dabrafenib in mutant BRAF-driven melanomas. Methods to understand how resistance develops are important to optimize the clinical use of RAF inhibitors in patients. Here, we report the development of a novel ERK1/2 reporter system that provides a noninvasive, quantitative, and temporal analysis of RAF inhibitor efficacy in vivo. Use of this system revealed heterogeneity in the level of ERK1/2 reactivation associated with acquired resistance to RAF inhibition. We identified several distinct novel and known molecular changes in resistant tumors emerging from treatment-naïve cell populations including BRAF V600E variants and HRAS mutation, both of which were required and sufficient for ERK1/2 reactivation and drug resistance. Our work offers an advance in understanding RAF inhibitor resistance and the heterogeneity in resistance mechanisms, which emerge from a malignant cell population.

Melanoma adapts to RAF/MEK inhibitors through FOXD3-mediated upregulation of ERBB3

The mechanisms underlying adaptive resistance of melanoma to targeted therapies remain unclear. By combining ChIP sequencing with microarray-based gene profiling, we determined that ERBB3 is upregulated by FOXD3, a transcription factor that promotes resistance to RAF inhibitors in melanoma. Enhanced ERBB3 signaling promoted resistance to RAF pathway inhibitors in cultured melanoma cell lines and in mouse xenograft models. ERBB3 signaling was dependent on ERBB2; targeting ERBB2 with lapatinib in combination with the RAF inhibitor PLX4720 reduced tumor burden and extended latency of tumor regrowth in vivo versus PLX4720 alone. These results suggest that enhanced ERBB3 signaling may serve as a mechanism of adaptive resistance to RAF and MEK inhibitors in melanoma and that cotargeting this pathway may enhance the clinical efficacy and extend the therapeutic duration of RAF inhibitors.

Downregulation of Noxa by RAF/MEK inhibition counteracts cell death response in mutant B-RAF melanoma cells

FDA approval of new therapies in 2011 has greatly expanded the treatment options for metastatic melanoma. Patients with V600 mutant v-raf murine sarcoma viral oncogene homolog B1 (B-RAF) positive metastatic melanoma are now treated with the RAF inhibitor, vemurafenib (Zelboraf) as a first line therapy. Vemurafenib decreases tumor size by at least 30% in approximately 50% of patients and increases progression-free survival and overall patient survival compared to the previous standard-of-care, dacarbazine. However, some patients treated with vemurafenib fail to show significant tumor shrinkage, and most patients who initially respond to the drug eventually show disease progression. Therefore, there is a clinical need to improve efficacy and prevent resistance to vemurafenib. It has been previously shown that cell death resulting from RAF/mitogen-activated protein kinase kinase (MEK) inhibition is largely dependent on increased expression of pro-apoptotic, Bcl-2 homology domain (BH3)-only proteins, such as Bcl-2-like 11 (Bim-EL) and Bcl-2 modifying factor (Bmf). Here, we show that contrary to expression of Bim-EL and Bmf, the pro-apoptotic, BH3-only protein, phorbol-12-myristate-13-acetate-induced protein 1 (Noxa), is strongly downregulated after RAF/MEK inhibition. This downregulation occurs at both the protein and mRNA level of expression and is associated with the inhibition of cell cycle progression. Restoring expression of Noxa in combination with RAF/MEK inhibition enhances cell death. Co-expression of the pro-survival, B-cell CLL/lymphoma 2 (Bcl-2) family member, myeloid cell leukemia sequence 1 (Mcl-1), with Noxa fully mitigates the enhanced cell death associated with increased Noxa expression. These data indicate that manipulating the Noxa/Mcl-1 axis may enhance the efficacy of RAF/MEK inhibitors.

Upcoming strategies for the treatment of metastatic melanoma

Prognosis for advanced and metastatic melanoma is poor, with a 5-year survival of 78, 59 and 40% for patients with stage IIIA, IIIB and IIIC, respectively, and a 1-year survival of 62% for M1a, 53% for M1b and 33% for M1c. The unsatisfactory results of actual standard therapies for metastatic melanoma highlight the need for effective new therapeutic strategies. Several drugs, including BRAF, KIT and MEK inhibitors, are currently being evaluated after promising data from Phase I and Phase II studies; Vemurafenib, a BRAF-inhibitor agent, has been approved by the Food and Drug Administration (FDA) for the treatment of patients with unresectable or metastatic melanoma with the BRAF V600E mutation after a significant impact on both progression-free and overall survival was demonstrated compared with dacarbazine in a Phase III trial. Ipilimumab, an immunotherapeutic drug, has proven to be capable of inducing long-lasting responses and was approved for patients with advanced melanoma in first- and second-line treatment by the FDA and in second-line treatment by the European Medicines Agency. Furthermore, a significant survival benefit of the combination of ipilimumab with dacarbazine compared with dacarbazine alone for first-line treatment was reported. In the near future, patients with BRAF mutations could have the chance to benefit from treatment with BRAF inhibitors; patients harboring BRAF or NRAS mutations could be treated with MEK inhibitors; finally, the subgroup of patients with acral, mucosal or chronic sun-damaged melanoma harboring a KIT mutation could benefit from KIT inhibitors. Ipilimumab could become a standard treatment for metastatic melanoma, both as a single agent and in combination; its efficacy has been proven, and researchers should now address their efforts to understanding the predictive variables of response to treatment.

FOXD3 regulates migration properties and Rnd3 expression in melanoma cells

Forkhead transcription factor, Foxd3, plays a critical role during development by controlling the lineage specification of neural crest cells. Notably, Foxd3 is highly expressed during the wave of neural crest cell migration that forms peripheral neurons and glial cells but is downregulated prior to migration of cells that give rise to the melanocytic lineage. Melanoma is the deadliest form of skin cancer and is derived from melanocytes. Recently, we showed that FOXD3 expression is elevated following the targeted inhibition of the B-RAF-MEK (MAP/ERK kinase)-ERK (extracellular signal-regulated kinase)1/2 pathway in mutant B-RAF melanoma cells. Because melanoma cells are highly migratory and invasive in a B-RAF-dependent manner, we explored the role of FOXD3 in these processes. In this study, we show that ectopic FOXD3 expression inhibits the migration, invasion, and spheroid outgrowth of mutant B-RAF melanoma cells. Upregulation of FOXD3 expression following inhibition of B-RAF and MEK correlates with the downregulation of Rnd3, a Rho GTPase and inhibitor of RhoA-ROCK signaling. Indeed, expression of FOXD3 alone was sufficient to downregulate Rnd3 expression at the mRNA and protein levels. Mechanistically, FOXD3 was found to be recruited to the Rnd3 promoter. Inhibition of ROCK partially restored migration in FOXD3-expressing cells. These data show that FOXD3 expression downregulates migration and invasion in melanoma cells and Rnd3, a target known to be involved in these properties.

Crosstalk of the EphA2 receptor with a serine/threonine phosphatase suppresses the Akt-mTORC1 pathway in cancer cells

Receptor tyrosine kinases of the Eph family play multiple roles in the physiological regulation of tissue homeostasis and in the pathogenesis of various diseases, including cancer. The EphA2 receptor is highly expressed in most cancer cell types, where it has disparate activities that are not well understood. It has been reported that interplay of EphA2 with oncogenic signaling pathways promotes cancer cell malignancy independently of ephrin ligand binding and receptor kinase activity. In contrast, stimulation of EphA2 signaling with ephrin-A ligands can suppress malignancy by inhibiting the Ras-MAP kinase pathway, integrin-mediated adhesion, and epithelial to mesenchymal transition. Here we show that ephrin-A1 ligand-dependent activation of EphA2 decreases the growth of PC3 prostate cancer cells and profoundly inhibits the Akt-mTORC1 pathway, which is hyperactivated due to loss of the PTEN tumor suppressor. Our results do not implicate changes in the activity of Akt upstream regulators (such as Ras family GTPases, PI3 kinase, integrins, or the Ship2 lipid phosphatase) in the observed loss of Akt T308 and S473 phosphorylation downstream of EphA2. Indeed, EphA2 can inhibit Akt phosphorylation induced by oncogenic mutations of not only PTEN but also PI3 kinase. Furthermore, it can decrease the hyperphosphorylation induced by constitutive membrane-targeting of Akt. Our data suggest a novel signaling mechanism whereby EphA2 inactivates the Akt-mTORC1 oncogenic pathway through Akt dephosphorylation mediated by a serine/threonine phosphatase. Ephrin-A1-induced Akt dephosphorylation was observed not only in PC3 prostate cancer cells but also in other cancer cell types. Thus, activation of EphA2 signaling represents a possible new avenue for anti-cancer therapies that exploit the remarkable ability of this receptor to counteract multiple oncogenic signaling pathways.

Treatment of cutaneous melanoma: current approaches and future prospects

Melanoma is the most aggressive and deadly type of skin cancer. Surgical resection with or without lymph node sampling is the standard of care for primary cutaneous melanoma. Adjuvant therapy decisions may be informed by careful consideration of prognostic factors. High-dose adjuvant interferon alpha-2b increases disease-free survival and may modestly improve overall survival. Less toxic alternatives for adjuvant therapy are currently under study. External beam radiation therapy is an option for nodal beds where the risk of local recurrence is very high. In-transit melanoma metastases may be treated locally with surgery, immunotherapy, radiation, or heated limb perfusion. For metastatic melanoma, the options include chemotherapy or immunotherapy; targeted anti-BRAF and anti-KIT therapy is under active investigation. Standard chemotherapy yields objective tumor responses in approximately 10%-20% of patients, and sustained remissions are uncommon. Immunotherapy with high-dose interleukin-2 yields objective tumor responses in a minority of patients; however, some of these responses may be durable. Identification of activating mutations of BRAF, NRAS, c-KIT, and GNAQ in distinct clinical subtypes of melanoma suggest that these are molecularly distinct. Emerging data from clinical trials suggest that substantial improvements in the standard of care for melanoma may be possible.

Treatment of cutaneous melanoma: current approaches and future prospects

Melanoma is the most aggressive and deadly type of skin cancer. Surgical resection with or without lymph node sampling is the standard of care for primary cutaneous melanoma. Adjuvant therapy decisions may be informed by careful consideration of prognostic factors. High-dose adjuvant interferon alpha-2b increases disease-free survival and may modestly improve overall survival. Less toxic alternatives for adjuvant therapy are currently under study. External beam radiation therapy is an option for nodal beds where the risk of local recurrence is very high. In-transit melanoma metastases may be treated locally with surgery, immunotherapy, radiation, or heated limb perfusion. For metastatic melanoma, the options include chemotherapy or immunotherapy; targeted anti-BRAF and anti-KIT therapy is under active investigation. Standard chemotherapy yields objective tumor responses in approximately 10%-20% of patients, and sustained remissions are uncommon. Immunotherapy with high-dose interleukin-2 yields objective tumor responses in a minority of patients; however, some of these responses may be durable. Identification of activating mutations of BRAF, NRAS, c-KIT, and GNAQ in distinct clinical subtypes of melanoma suggest that these are molecularly distinct. Emerging data from clinical trials suggest that substantial improvements in the standard of care for melanoma may be possible.

Cyclin D1 and D3 expression in melanocytic skin lesions

Cyclins, cyclin-dependent kinases, as well as proteins cooperating with them are responsible for cell cycle regulation which is crucial for normal development, injury repair, and tumorigenesis. D-type cyclins regulate G1 cell cycle progression by enhancing the activities of cyclin-dependent kinases, and their expression is frequently altered in tumors. Disturbances in cyclin expression were also reported in melanocytic skin lesions. The objective of the study was to evaluate the expression of cyclins D1 and D3 in common, dysplastic, and malignant melanocytic skin lesions. Forty-eight melanocytic skin lesions including common nevi (10), dysplastic nevi (24), and melanomas (14) were diagnosed by dermoscopy and excised. Expression of cyclin D1 and D3 was detected by immunohistochemistry and quantified as percentage of immunostained cell nuclei in each sample. In normal skin, expression of cyclins D1 and D3 was not detected. The mean percentage of cyclin D1-positive nuclei was 7.75% for melanoma samples, 5% for dysplastic nevi samples, and 0.34% for common nevi samples. For cyclin D3, the respective values were 17.8, 6.4, and 1.8%. Statistically significant differences in cyclin D1 expression were observed between melanomas and common nevi as well as between dysplastic and common nevi (p = 0.0001), but not between melanomas and dysplastic nevi. Cyclin D3 expression revealed significant differences between all investigated lesion types (p = 0.0000). The mean cyclin D1 and D3 scores of melanomas with Breslow thickness <1 mm and >1 mm were not significantly different. G1/S abnormalities are crucial for the progression of malignant melanoma, and enhanced cyclin D1 and D3 expression leading to increased melanocyte proliferation is observed in both melanoma and dysplastic nevi. In histopathologically ambiguous cases, lower cyclin D3 expression in dysplastic nevi can be a diagnostic marker for that lesion type.

Phosphatidylinositol-3-kinase-AKT pathway, phospho-JUN and phospho-JNK expression in spontaneously arising bovine urinary bladder tumours

The aetiopathogenesis of urinary bladder tumours in cattle involves prolonged ingestion of bracken fern and infection by bovine papillomavirus types 1 or 2 (BPV-1/2). E5, the major BPV-1/2 oncoprotein, binds to the activated platelet-derived growth factor beta receptor (pPDGF-betaR), inducing cell transformation in vitro and spontaneously arising urinary bladder tumours. The aim of this study was to assess whether the 85 kDa regulatory subunit (p85) of the phosphatidylinositol-3-kinase (PI3K)-AKT pathway and other transforming signals phospho-JUN (pJUN) and phospho-JUN N-terminal kinases (pJNK) may be important in the development of BPV-associated urothelial carcinomas. A physical interaction between the pPDGF-betaR and PI3K was shown in four tumours and two samples of normal bladder tissue by co-immunoprecipitation and western blotting. There was greater expression of the PI3K-AKT-cyclin D3 molecular pathway downstream to the activation of pPDGF-betaR in neoplastic compared with normal tissue. pJNK and pJUN were overexpressed in samples of tumour compared with normal mucosal tissue. These findings provide new insights into the aetiopathogenic mechanisms underlying naturally occurring bovine urothelial carcinogenesis and contribute to understanding of the role of E5 oncoprotein in naturally occurring tumorigenesis.

FOXD3 is a mutant B-RAF-regulated inhibitor of G(1)-S progression in melanoma cells

The forkhead box transcription factor FOXD3 is a stemness factor that prevents the production of melanocyte progenitors from the developing neural crest; however, its role in human cancers is not known. Transformation of melanocytes gives rise to melanoma. In two thirds of melanomas, the serine/threonine kinase B-RAF is mutated to a constitutively active form. Here, we show that FOXD3 levels are upregulated following attenuation of B-RAF and mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK) signaling in mutant B-RAF harboring human melanoma cells. This effect was selective because FOXD3 was not upregulated following MEK inhibition in wild-type B-RAF melanoma cells and mutant B-RAF thyroid carcinoma cells. Ectopic FOXD3 expression potently inhibited melanoma cell growth without altering mutant B-RAF activation of ERK1/2. Inhibition of cell growth was due to a potent G(1) cell cycle arrest and was associated with p53-dependent upregulation of p21(Cip1). FOXD3-induced cell cycle arrest was prevented by p53 depletion and, to a lesser extent, p21(Cip1) depletion. These studies show that FOXD3 is suppressed by B-RAF, uncover a novel role and mechanism for FOXD3 as a negative cell cycle regulator, and have implications for the repression of melanocytic lineage cells.

Melanoma biomarkers: current status and utility in diagnosis, prognosis, and response to therapy

Melanoma is the most devastating form of skin cancer and represents a leading cause of cancer death, particularly in young adults. As even relatively small melanomas can readily metastasize, accurate staging of progression is critical. Diagnosis is typically made on the basis of histopathologic criteria; with tumor thickness (Breslow), invasion level (Clark), ulceration, and the extent of lymph node involvement being important prognostic indicators. However, histologic criteria alone cannot diagnose all melanomas and there are often problems in distinguishing subsets of benign nevi from melanoma. There also exists a group of patients with thin primary melanomas for whom surgery should be curative but who ultimately go on to develop metastases. Therefore, there is an urgent need to develop molecular biomarkers that identify melanoma patients with high-risk primary lesions to facilitate greater surveillance and possible adjuvant therapy. The advent of large-scale genomic profiling of melanoma is revealing considerable heterogeneity, suggesting that melanomas could be subgrouped according to their patterns of oncogenic mutation and gene expression. It is hoped that this subgrouping will allow for the personalization of melanoma therapy using novel molecularly targeted agents. Much effort is now geared toward defining the genetic markers that may predict response to targeted therapy agents as well as identifying pharmacodynamic markers of therapy response. In this review, we discuss the utility of melanoma biomarkers for diagnosis and prognosis and suggest how novel molecular signatures can help guide both melanoma diagnosis and therapy selection.

Activated platelet-derived growth factor beta receptor expression, PI3K-AKT pathway molecular analysis, and transforming signals in equine sarcoids

The equine sarcoid is the most common dermatologic neoplasm reported in horses. Bovine papillomavirus (BPV) types 1 and 2 are associated with sarcoids, in which the expression of the major transforming oncoprotein (E5) is often recorded. The transformation activity of the virus is due to the binding of the E5 to the platelet-derived growth factor beta receptor (PDGFbeta-r). In the present study, we show by Western blot in 4 sarcoid samples and 3 normal equine skin samples that the PDGFbeta-r is more phosphorylated in sarcoid tissue than in normal skin (P < .001). Furthermore, the physical interaction between the activated receptor and the 85-kDa regulatory subunit (p85) of phosphatidylinositol-3-kinase (PI3K) is shown by coimmunoprecipitation. The PI3K-AKT-cyclin D3 molecular pathway downstream to the activation of the PDGFbeta-r is shown to be expressed, and the amount of the investigated molecules is higher than normal (P < .001), suggesting an activation of these effectors in sarcoids. Further, we demonstrate that phospho-JNK and phospho-JUN are more expressed in sarcoids than in normal skin. Our results provide new insights into the pathogenesis of equine sarcoids and support the validity of this in-vivo model to further characterize the molecular pathways underlying BPV E5-induced carcinogenesis.

Phorbol 12-myristate 13-acetate inhibits FRO anaplastic human thyroid cancer cell proliferation by inducing cell cycle arrest in G1/S phase: evidence for an effect mediated by PKCdelta

Phorbol 12-myristate 13-acetate (PMA) is known to affect a variety of cellular processes, including cell proliferation, differentiation, and migration. PMA has been shown to promote antiproliferative and antimigratory effects in many types of cancer cells. Our findings show that PMA induced a strong antiproliferative effect in two anaplastic (FRO and ARO) and one follicular (ML-1) thyroid cancer cell lines, and increased the fraction of FRO cells in G1 phase of the cell cycle. The fractions in the S and G2 phases were decreased. Moreover, PMA evoked a significant increase in the levels of the cell cycle regulators p21Waf1/Cip1 and p27Kip1. The levels of cyclin D3 and the cyclin-dependent kinases cdk4 and cdk6 decreased, as did the phosphorylation of the Rb-protein. PMA did not induce apoptosis. PMA stimulated the translocation of protein kinase C (PKC) alpha, betaI and delta isoforms to the cell membrane. PKCdelta small interfering RNA attenuated the PMA-induced antiproliferative effect and prevented the upregulation of p21Waf1/Cip1 and p27Kip1. Prolonged stimulation with PMA decreased the phosphorylation of mitogen-activated protein (MAP) kinase. PMA also decreased the phosphorylation of Akt and evoked a biphasic change in the phosphorylation of the forkhead box class-O protein (FOXO): an increase in phosphorylation, followed by a dephosphorylation. In addition, PMA inhibited FRO, ARO and ML-1 cell migration toward serum. The inactive phorbol ester analog 4alpha-phorbol and the diacylglycerol analog 1,2-dioctanoyl-sn-glycerol were without an effect on proliferation and migration. The results indicate that PMA is an effective inhibitor of thyroid cancer cell proliferation and migration by a mechanism involving PKC-MAP kinase/Akt and FOXO signaling.

Detection of copy number alterations in metastatic melanoma by a DNA fluorescence in situ hybridization probe panel and array comparative genomic hybridization: a southwest oncology group study (S9431)

PURPOSE

Gene copy number alteration (CNA) is common in malignant melanoma and is associated with tumor development and progression. The concordance between molecular cytogenetic techniques used to determine CNA has not been evaluated on a large set of loci in malignant melanoma.

EXPERIMENTAL DESIGN

A panel of 16 locus-specific fluorescence in situ hybridization (FISH) probes located on eight chromosomes was used to identify CNA in touch preparations of frozen tissue samples from 19 patients with metastatic melanoma (SWOG-9431). A subset (n = 11) was analyzed using bacterial artificial chromosome (BAC) array comparative genomic hybridization (aCGH) of DNA isolated directly from touch-preparation slides.

RESULTS

By FISH, most samples showed loss near or at WISP3/6p21, CCND3/6q22, and CDKN2A/9p21 (>75% of samples tested). More than one third of CDKN2A/9p21 losses were biallelic. Gains of NEDD9/6p24, MET/7q31, and MYC/8q24 were common (57%, 47%, and 41%, respectively) and CNA events involving 9p21/7p12.3 and MET were frequently coincident, suggesting gain of the whole chromosome 7. Changes were confirmed by aCGH, which also uncovered many discreet regions of change, larger than a single BAC. Overlapping segments observed in >45% of samples included many of the loci analyzed in the FISH study, in addition to other WNT pathway members, and genes associated with TP53 pathways and DNA damage response, repair, and stability.

CONCLUSIONS

This study outlines a set of CNAs at the gene and regional level, using FISH and aCGH, which may provide a benchmark for future studies and may be important in selection of individual therapy for patients with metastatic malignant melanoma.

Transforming signals resulting from sustained activation of the PDGFbeta receptor in mortal human fibroblasts

The platelet-derived growth factor beta receptor (PDGFbetaR) plays an important role in proliferation and motility of fibroblasts. We have been investigating the effects of sustained PDGFbetaR activation in mortal human diploid fibroblasts (HDFs), which are typically difficult to transform. We have previously shown that the bovine papillomavirus E5 protein, through its ability to crosslink and constitutively activate the PDGFbetaR, induces morphological transformation, enhanced growth and loss of contact inhibition (focus formation) in HDFs. Here, we characterized two E5 mutants as being severely defective for focus formation but still competent for enhanced growth, suggesting that proliferation is insufficient for loss of contact inhibition. These E5 mutants were then used in a comparative study to distinguish the PDGFbetaR signaling intermediates required for the enhanced growth phenotype from those required for focus formation. Our data suggested that a PI 3-kinase (PI3K)-AKT-cyclin D3 pathway, a Grb2-Gab1-SHP2 complex and JNK played a role in the enhanced growth phenotype. However, a SHP2-p66Shc-p190BRhoGAP complex and ROCK were implicated exclusively in focus formation. We speculate that a SHP2-p66Shc-p190BRhoGAP signaling complex recruited to the activated PDGFbetaR promotes a distinct Rho-dependent process required for focus formation but not growth of HDFs.

Understanding signaling cascades in melanoma

Understanding regulatory pathways involved in melanoma development and progression has advanced significantly in recent years. It is now appreciated that melanoma is the result of complex changes in multiple signaling pathways that affect growth control, metabolism, motility and the ability to escape cell death programs. Here we review the major signaling pathways currently known to be deregulated in melanoma with an implication to its development and progression. Among these pathways are Ras, B-Raf, MEK, PTEN, phosphatidylinositol-3 kinase (PI3Ks) and Akt which are constitutively activated in a significant number of melanoma tumors, in most cases due to genomic change. Other pathways discussed in this review include the [Janus kinase/signal transducer and activator of transcription (JAK/STAT), transforming growth factor-beta pathways which are also activated in melanoma, although the underlying mechanism is not yet clear. As a paradigm for remodeled signaling pathways, melanoma also offers a unique opportunity for targeted drug development.

E1AF promotes breast cancer cell cycle progression via upregulation of Cyclin D3 transcription

E1AF transcription factor, a member of Ets family, is deregulated in many tumors and widely known to play critical roles in tumor metastasis via directly binding to the promoter of genes involved in tumor migration and invasion. Here, we found that E1AF overexpression promoted breast cancer cell cycle progression and growth in vivo as well as the transcription of cell cycle-related protein Cyclin D3. And, the interference of Cyclin D3 expression by transfecting with Cyclin D3 RNAi inhibited the positive role of E1AF in cell cycle progression. We further showed that decreasing the expression of E1AF by E1AF RNAi reduced Cyclin D3 transcription and expression, and inhibited cell cycle progression that was abrogated by Cyclin D3 overexpression. Taken together, E1AF increases cell cycle progression via upregulation of Cyclin D3 transcription, which elicits a new mechanism of breast cancer growth and a new mechanism of Cyclin D3 transcription.