Expression patterns of cyclin D1 and related proteins regulating G1-S phase transition in uveal melanoma and retinoblastoma

Abstract

Background/aims-A checkpoint mechanism in late G1, whose regulation via loss of retinoblastoma protein (pRB) or p16, or overexpression of cyclin D1 or cyclin dependent kinase 4 (CDK4), has been proposed to constitute a common pathway to malignancy. The aims of this study were (a) to compare markers of cell cycle G1-S phase transition in an intraocular tumour with known pRB deficiency (retinoblastoma) and compare it with one with an apparently functional pRB (uveal melanoma); (b) to determine if one of these markers may have a role in the pathogenesis of uveal melanoma; and (c) to determine if there is a diVerence in cell cycle marker expression following treatment of uveal melanoma and retinoblastoma. Methods-90 eyes were enucleated from 89 patients for retinoblastoma (n=24) or for choroidal or ciliary body melanoma (n=66). Conventional paraYn sections were assessed for cell type and degree of diVerentiation. Additional slides were investigated applying standard immunohistochemical methods with antibodies specific for cyclin D1 protein, pRB, p53, p21, p16, BCL-2, and MIB-1. Results-Cyclin D1 protein and pRB were negative in retinoblastoma using the applied antibodies. In contrast, cyclin D1 protein expression was observed in 65% of uveal melanomas; a positive correlation between cyclin D1 cell positivity and tumour cell type, location, growth fraction, as well as with pRB positivity was observed. p53, p21, and p16 could be demonstrated in both tumours. An inverse relation between p53 and p21 expression was demonstrated in most choroidal melanomas and in some retinoblastomas. Apart from a decrease in the growth fractions of the tumours as determined by MIB-1, a significant diVerence in the expression of G1-S phase transition markers in vital areas of uveal melanoma and retinoblastoma following treatment with radiotherapy and/or chemotherapy was not observed. Conclusion-Retinoblastomas and uveal melanomas, two tumours of diVering pRB status, diVer also in their immunohistochemical pattern for markers of the G1-S phase transition of the cell cycle. The results of the present study support the concept of (a) an autoregulatory loop between pRB and cyclin D1 in tumours with a functional pRB and the disruption of this loop in the presence of pRB mutation, as well as (b) a checkpoint mechanism in late G1, whose regulation via loss of p16 or pRB, or overexpression of cyclin D1 constitutes a common pathway to malignancy. Further, the results raise the possibility of cyclin D1 overexpression having a role in the pathogenesis of uveal melanoma. (Br J Ophthalmol 1998;82:961-970)

Molecular pathology of uveal melanoma

“…[11][12][13]29,30,90 The Rb protein is constitutively hyperphosphorylated and functionally inactivated in most UM, probably as a result of cyclin D1 overexpression in about 65% of cases. 12,14,15 ( Figure 1; Table 1) The role of CDKN2A promoter hypermethylation, as an additional mechanism of Rb inactivation, is controversial as the frequency of hypermethylation of this gene varies between 4 and 33% of UM. 12,[14][15][16]48,74 Increased cyclin D1 protein expression has been associated with larger tumour basal diameter, epithelioid cell type, and poor prognosis.…”

“…The p53 pathway is functionally blocked by its inhibitor MDM2 [13][14][15]29,30 BCL-2 Defects in the Bcl2 pathway in UM contribute to apoptosis resistance 11,14,29 PTEN downregulation The PI3K-AKT prosurvival pathway is constitutively activated in UM to avoid apoptosis 19,20 Produce insulin-like growth factor (IGF- …”

“…79 This has been observed in longitudinal studies using next-generation sequencing in paired primary and metastatic carcinomas, 89 and warrants further investigation using such techniques in UM. The retinoblastoma tumour suppressor pathway is disrupted in most UM either through: hyperphosphorylation of Rb; elevated expression of cyclin D1; or through methylation and inactivation of the INK4A gene [11][12][13][14][15][16] 2. Self-sufficiency in growth signals Gain of cell cycle stimulator-activation of pathways The PI3K-AKT prosurvival pathway is constitutively activated in UM.…”

Dual inhibition of protein kinase C and p53-MDM2 or PKC and mTORC1 are novel efficient therapeutic approaches for uveal melanoma

“…Optimization of dose and dosing regimen as well as the use of alternative MEKi or PKCi may further improve the therapeutic index and clinical benefit to patients of this combination. Because of high cyclin D1 and Rb expressions observed in UM [29] [30][31], we evaluated the combination of PKCi + CDK4/6i using AEB071 and LEE011 compounds. Only www.impactjournals.com/oncotarget a limited efficacy of LEE011 was observed and no clear evidence of increased efficacy combining it with AEB071 was detected, indicating that co-inhibition of PKC and CDK4/6 is not an optimal strategy for treating UM.…”

“…Moreover, a synergistic effect has been described after combination of AEB071 with the PI3Kα inhibitor BYL719 in vitro and in vivo [27]. Second, while p53 mutations are not common in UM [28], several studies have shown that UM have an inactivated p53 pathway, due to (i) high expression of the protein MDM2 [28][29] [30][31] [32] and (ii) downregulation of the protein PERP in aggressive UM [33] [34]. Furthermore, the MDM2 inhibitor Nutlin-3 was shown to reduce UM cell proliferation in a p53-dependent manner [35].…”