Chromatin remodeling and Rb activity.

Progression of cells through the cell cycle is central to normal cell proliferation, and checkpoints that regulate this cycle are targets of tumorigenic mutations. One of these checkpoints is the Rb family of proteins that seems to regulate exit of cells from both G(1) and S phase of the cell cycle. Recent studies have linked the function of the Rb family to chromatin remodeling enzymes.

Rb function in cell-cycle regulation and apoptosis.

Loss of cell-cycle control is a hallmark of neoplastic cells. One regulator of the critical G1 to S-phase transition in the cell cycle is the retinoblastoma tumour suppressor protein Rb, which interacts with the E2F family of cell-cycle transcription factors to repress gene transcription required for this transition. Through its interaction with E2F, Rb also regulates genes that control apoptosis. Here we review the roles of Rb in regulating the cell cycle and apoptosis and discuss recent results linking these Rb functions to chromatin-remodelling enzymes.

Abnormalities in structure and expression of the human retinoblastoma gene in SCLC.

Small cell lung cancer (SCLC) has been associated with loss of heterozygosity at several distinct genetic loci including chromosomes 3p, 13q, and 17p. To determine whether the retinoblastoma gene (Rb) localized at 13q14, might be the target of recessive mutations in lung cancer, eight primary SCLC tumors and 50 cell lines representing all major histologic types of lung cancer were examined with the Rb complementary DNA probe. Structural abnormalities within the Rb gene were observed in 1/8 (13%) primary SCLC tumors, 4/22 (18%) SCLC lines, and 1/4 (25%) pulmonary carcinoid lines (comparable to the 20 to 40% observed in retinoblastoma), but were not detected in other major types of lung cancer. Rb messenger RNA expression was absent in 60% of the SCLC lines and 75% of pulmonary carcinoid lines, including all samples with DNA abnormalities. In contrast, Rb transcripts were found in 90% of non-SCLC lung cancer lines and in normal human lung. The finding of abnormalities of the Rb gene in SCLC and pulmonary carcinoids (both neuroendocrine tumors) suggests that this gene may be involved in the pathogenesis of a common adult malignancy.

Inactivation of retinoblastoma protein in uveal melanoma by phosphorylation of sites in the COOH-terminal region.

Uveal melanoma is the most common malignancy of the eye, but little is known about its underlying genetic defects. Melanomas of uveal origin, unlike those of the skin, are rarely familial and have not been linked consistently to mutations in tumor suppressor genes. Here, we investigated the Rb pathway in uveal melanoma. Most tumors displayed strong immunostaining for Rb and p16, suggesting that they were not mutationally inactivated. However, Rb was frequently phosphorylated at serine-807 and serine-811, and cyclin D1 was expressed in many of the tumors. Mutation of these serine residues prevented cyclin D-dependent phosphorylation from inactivating Rb in cultured cells. We conclude that Rb is frequently inactivated in uveal melanoma by phosphorylation of residues in the COOH-terminal region that regulate its activity, and one mechanism for this phosphorylation is overexpression of cyclin D.

Local carboplatin therapy in transgenic murine retinoblastoma.

PURPOSE: To determine the efficacy and toxicity associated with intraocular delivery of carboplatin in the treatment of murine transgenic hereditary retinoblastoma. METHODS: Forty-eight transgenic BLH-SV40 Tag retinoblastoma mice were administered five intravitreal injections of carboplatin in one eye. After 12 weeks, the eyes were examined histopathologically to evaluate tumor burden. Twelve rabbits were administered intravitreal injections of carboplatin in one eye, after which they underwent serial electroretinography. All experimental and control eyes were obtained for histopathology and electron microscopy. RESULTS: A dose-dependent inhibition of intraocular tumor growth by carboplatin was observed in transgenic retinoblastoma mice. Tumor development was inhibited in 50% of the mouse eyes at doses of 1.4 micrograms. In rabbits, retinal toxicity resulted when intravitreal injections of carboplatin were administered at doses of 10 micrograms or higher. CONCLUSIONS: Local delivery of carboplatin in serial doses effectively inhibits intraocular tumor growth in a dose-dependent manner in transgenic murine retinoblastoma.

Molecular basis of low-penetrance retinoblastoma.

Retinoblastoma is a malignant tumor of the retina that occurs primarily in young children as a result of mutations in the retinoblastoma gene (RB), the first tumor suppressor gene to be identified. In about 35% to 40% of patients with retinoblastoma, an RB gene mutation is present in the germline, resulting in hereditary transmission of the disease. Most families with hereditary retinoblastoma demonstrate autosomal dominant inheritance with almost complete penetrance and high expressivity. However, some families display an inheritance pattern characterized by reduced penetrance and expressivity. Recent advances in our understanding of the structure and function of the retinoblastoma protein (pRB) now provide new insights into the molecular basis of this low-penetrance form of retinoblastoma. Low-penetrance retinoblastoma mutations either cause a reduction in the amount of normal pRB that is produced (class 1 mutations) or result in a partially functional mutant pRB (class 2 mutations).

Pars plana vitrectomy in the management of phakic and pseudophakic malignant glaucoma.

OBJECTIVE: To determine the indications for and outcome of pars plana vitrectomy in the management of phakic and pseudophakic malignant glaucoma. DESIGN: Retrospective review. SETTING: Tertiary referral ophthalmic hospital. PATIENTS: Twenty-two patients (24 eyes) who underwent pars plana vitrectomy in the management of malignant glaucoma. RESULTS: Fourteen eyes were phakic and 10 were pseudophakic at the initial vitrectomy. The primary indication for vitrectomy was failure of other therapies. In phakic eyes, the initial vitrectomy was successful in terminating malignant glaucoma without further surgery in 7 (100%) of 7 eyes that underwent lensectomy and in 5 (71%) of 7 eyes that not did not undergo lensectomy. The primary indication for lensectomy was corneal edema caused by lens-corneal touch. In pseudophakic eyes, the initial vitrectomy was successful in 9 (90%) of 10 eyes. Removal of the intraocular lens was performed in 1 eye. Perioperative complications included transient serous choroidal detachment in 2 eyes, transient exudative retinal detachment in 1 eye, and suprachoroidal hemorrhage in 1 eye. CONCLUSIONS: Pars plana vitrectomy is effective in treating phakic and pseudophakic malignant glaucoma. Success is contingent on establishing a pathway for aqueous flow into the anterior chamber, which usually is accompanied by intraoperative deepening of the anterior chamber. In phakic eyes, lensectomy may be considered for marked corneal edema, for dense cataract, or when the anterior chamber will not deepen during vitrectomy.

Tumor suppressor genes in ophthalmology.

Tumor suppressor genes have a diversity of functions, but they have in common the property of inhibiting neoplastic transformation. When they become inactivated, a constraint is removed that allows cells to grow inappropriately. Mutations in these genes are now thought to be the initiating events in most cancers. The first tumor suppressor gene was discovered through its role in retinoblastoma, and many other tumor suppressor genes also have important ophthalmic manifestations. The first group of tumor suppressor genes to be discussed are those involved in retinoblastoma and uveal melanoma. These are among the most frequently mutated genes in human cancer and are key regulators of growth and homeostasis. The second group of genes is associated with specific hereditary tumor syndromes with ophthalmic manifestations. These genes function in a variety of molecular pathways and are associated with neoplastic and non-neoplastic abnormalities in restricted tissue distributions. Research on tumor suppressor genes continues to shed light on the molecular pathophysiology of ophthalmic tumors and will increasingly yield diagnostic and therapeutic applications.

Vitrectomy for diabetic macular edema associated with a thickened and taut posterior hyaloid membrane.

PURPOSE: To evaluate the surgical results in a series of patients with diabetic macular edema associated with traction from a thickened and taut posterior hyaloid membrane and to identify features associated with better visual outcome. METHODS: We reviewed the clinical records of ten consecutive patients who underwent pars plana vitrectomy in one eye for diabetic macular edema that was preoperatively attributed to thickening and traction of the posterior hyaloid membrane. RESULTS: Best-corrected, preoperative visual acuity was 20/200 in seven eyes, 20/300 in one eye, and 20/400 in two eyes. Intraoperatively, seven patients were found to have an attached posterior hyaloid membrane which was thickened and taut. Among these seven patients, postoperative best-corrected visual acuity improved by six lines in two eyes, by five lines in one eye, by two lines in one eye, and remained within one line of preoperative visual acuity in three eyes. The other three patients had an epiretinal membrane simulating an attached and thickened posterior hyaloid membrane. CONCLUSIONS: Vitrectomy effectively improved visual acuity in some eyes with diabetic macular edema associated with traction from a thickened and taut posterior hyaloid membrane. Despite careful preoperative examination with a fundus contact lens, however, in some patients it may be difficult to assess how the posterior hyaloid membrane contributes to the macular edema. In selected patients, early surgical intervention may be associated with better visual outcome.

Pars plana vitrectomy for chronic pseudophakic cystoid macular edema.

PURPOSE: We determined the efficacy of pars plana vitrectomy in a series of patients with chronic pseudophakic cystoid macular edema. METHODS: Clinical records were reviewed on 24 consecutive patients who underwent pars plana vitrectomy in one eye for chronic pseudophakic cystoid macular edema. All 24 patients had failed to improve on medical therapy and had preoperative evidence of either vitreous adhesions to anterior segment structures (23 eyes) or iris capture of the intraocular lens (one eye). RESULTS: The mean, best-corrected Snellen visual acuity was 20/190 preoperatively (median, 20/200; range, 20/50 to 3/200) and 20/52 postoperatively (median, 20/40; range, 20/20 to 20/400 [P < .0001]). Visual acuity improved postoperatively in all 24 eyes, with a mean improvement of 4.7 Snellen lines (range, one to eight lines). There was no highly significant difference in preoperative visual acuity (P = .41) or postoperative visual improvement (P = .17) between patients with anterior as opposed to posterior chamber intraocular lenses. Longer time interval from cataract surgery to vitrectomy did not correlate with less postoperative visual improvement. CONCLUSIONS: In pseudophakic eyes with chronic cystoid macular edema, vitreous adhesions to anterior segment structures, and visual loss that is unresponsive to medical therapy, pars plana vitrectomy with removal of these vitreous adhesions may lead to improved visual acuity.

Association between posterior uveal melanoma and iris freckles, iris naevi, and choroidal naevi.

AIM: To investigate the association between posterior uveal melanoma and iris freckles, iris naevi, and choroidal naevi. METHODS: Cross sectional study of 65 patients with posterior uveal melanoma and 218 controls. Iris colour, iris freckles, iris naevi, and choroidal naevi were recorded for each eye of each patient. RESULTS: Iris freckles were present in 40 (61.5%) patients with melanoma and 135 (61.9%) controls (p = 0.494). Iris naevi were present in four (6.2%) patients with melanoma and nine (4.1%) controls (p = 0.955). Choroidal naevi were present in 12 (18.5%) patients with melanoma and 38 (17.4%) controls (p = 0.815). CONCLUSION: This study did not detect an association between posterior uveal melanoma and iris freckles, iris naevi, or choroidal naevi.

Association between choroidal pigmentation and posterior uveal melanoma in a white population.

BACKGROUND/AIMS: It is well known that light skin pigmentation is a risk factor for cutaneous melanoma. The aim of this study was to investigate the analogous association between choroidal pigmentation and posterior uveal melanoma. METHODS: Cross sectional study of 65 consecutive patients diagnosed with posterior uveal melanoma (melanoma group) and 218 consecutive patients referred for general retinal evaluation (control group). All patients were white. A clinical grading system for estimating choroidal pigmentation was developed and histologically validated in seven patients. RESULTS: Melanoma patients with light iris colour were significantly more likely to have darker choroidal pigmentation than controls (p = 0.005). Darker choroidal pigmentation was associated histologically with increased density of choroidal melanocytes (p = 0.005). CONCLUSIONS: Increased choroidal pigmentation, as a result of an increase in the density of pigmented choroidal melanocytes, is not protective but may actually be a risk factor for the development of posterior uveal melanoma in white patients. This finding may have implications for understanding the pathogenesis of uveal melanoma.

Expression in lung cancer of a transcribed sequence at the DNF15S2 locus at chromosome 3P21.

The short arm of chromosome 3 undergoes genetic loss in virtually all small cell lung cancers (SCLC). The most frequently deleted region includes the DNF15S2 locus (mapped to 3p21), suggesting that a putative recessive SCLC gene might be located nearby. Using a DNA probe subcloned from the DNF15S2 locus, we identified a 3.0 kb mRNA species and isolated corresponding partial cDNA clones. Analysis of the nucleic acid sequence showed it to be the same as a recently published transcribed gene isolated from this chromosomal 3p21 region. To determine whether this gene might represent a "recessive oncogene" we examined a large number of SCLC and other human tumors and found no evidence for DNA rearrangements or inactivation of RNA expression. We discuss the significance of this transcribed gene and the DNF15S2 locus in tumorigenesis.

The molecular biology of retinoblastoma.

Retinoblastoma, a rare pediatric eye tumor, has served as an important model for the heritable predisposition to cancer. The retinoblastoma protein, Rb, functions as a tumor suppressor by controlling progression through the cell cycle. Rb function is regulated primarily by its phosphorylation state, which is determined by the complex interaction of multiple kinases and their inhibitors that together form the 'Rb pathway'. This pathway has been found to be functionally inactivated in almost all types of cancer. Despite recent advances in our understanding of Rb function, the precise role of Rb loss in the development of retinoblastoma remains unclear. Recent work in genetically altered mice has suggested that an additional mutation in another gene is required for retinal tumor formation. An alternative model presented here is based on the noncell-autonomous functions of Rb contributing to tumorigenesis.

Combined PKC and MEK inhibition for treating metastatic uveal melanoma.

Uveal melanoma (UM) is the most common primary intraocular malignancy and the second most common form of melanoma. UM has a strong tendency for metastatic disease, and no effective treatments have yet been identified. Activating oncogenic mutations are commonly found in GNAQ and GNA11 in UM, and inhibiting key downstream effectors of the GNAQ/11 signaling pathway represents a rational therapeutic approach for treating metastatic UM. Chen et al., doi:10.1038/onc.2013.418, now confirm activation of the MAPK and PKC pathways as a result of GNAQ and GNA11 activating mutations in melanocytes, and they demonstrate that MAPK activation occurs downstream of PKC activation. PKC inhibitors disrupt MAPK signaling and block proliferation of GNAQ/11 mutant UM cell lines and slow the in vivo growth of xenografted UM tumors without inducing their shrinkage. However, a combination of PKC and MEK inhibition led to sustained MAPK pathway inhibition and tumor regression in vivo. Hence, the authors concluded that MEK and PKC inhibition is synergistic, with superior efficacy to treatment of GNAQ/GNA11 mutant UMs with either drug alone.

p38 phosphorylates Rb on Ser567 by a novel, cell cycle-independent mechanism that triggers Rb-Hdm2 interaction and apoptosis.

The retinoblastoma protein (Rb) inhibits both cell division and apoptosis, but the mechanism by which Rb alternatively regulates these divergent outcomes remains poorly understood. Cyclin-dependent kinases (Cdks) promote cell division by phosphorylating and reversibly inactivating Rb by a hierarchical series of phosphorylation events and sequential conformational changes. The stress-regulated mitogen-activated protein kinase p38 also phosphorylates Rb, but it does so in a cell cycle-independent manner that is associated with apoptosis rather than with cell division. Here, we show that p38 phosphorylates Rb by a novel mechanism that is distinct from that of Cdks. p38 bypasses the cell cycle-associated hierarchical phosphorylation and directly phosphorylates Rb on Ser567, which is not phosphorylated during the normal cell cycle. Phosphorylation by p38, but not Cdks, triggers an interaction between Rb and the human homolog of murine double minute 2 (Hdm2), leading to degradation of Rb, release of E2F1 and cell death. These findings provide a mechanistic explanation as to how Rb regulates cell division and apoptosis through different kinases, and reveal how Hdm2 may functionally link the tumor suppressors Rb and p53.

Treatment outcomes for primary intraocular lymphoma: implications for external beam radiotherapy.

PURPOSE: Intravitreal chemotherapy for primary intraocular lymphoma (PIOL) increasingly is promoted as an alternative to radiotherapy, owing to putative high failure and complication rates of the latter modality. Our aim was to confirm whether these concerns about radiotherapy were borne out in patients treated at our institution over the last decade. DESIGN: Retrospective interventional case series. PARTICIPANTS: A total of 21 eyes of 12 patients with PIOL. METHODS: Comprehensive chart review of ophthalmologic and systemic manifestations, treatments, and outcomes. MAIN OUTCOME MEASURES: Radiation complications and local tumour control. RESULTS: Cytology-confirmed lymphoma involved one eye in three patients and both eyes in nine patients. Initial treatment included external beam radiotherapy and chemotherapy (six patients), chemotherapy alone (four patients), radiotherapy alone (one patient), and no treatment (one patient). Ocular relapses occurred in no patients receiving radiotherapy and in two patients who did not receive radiotherapy. Complications of radiotherapy included dry eye (four patients), cataract (four patients), and mild radiation retinopathy (two patients). CONCLUSIONS: Radiotherapy for PIOL is highly effective with acceptable complications. In the absence of a clear advantage to intravitreal chemotherapy, which involves repetitive injections and associated risks, radiotherapy may still be the most appropriate first-line treatment in most cases.