1009

CDH11

CAD11|CDHOB|OB|OSF-4;cadherin 11, type 2, OB-cadherin (osteoblast);CDH11;cadherin 11, type 2, OB-cadherin (osteoblast)

cadherin-11

16q21

protein-coding

Retinoblastoma is initiated by loss of both RB1 alleles. Previous studies have shown that retinoblastoma tumors also show further genomic gains and losses. We now define a 2.62 Mbp minimal region of genomic loss of chromosome 16q22, which is likely to contain tumor suppressor gene(s), in 76 retinoblastoma tumors, using loss of heterozygosity (30 of 76 tumors) and quantitative multiplex PCR (71 of 76 tumors). The sequence-tagged site WI-5835 within intron 2 of the cadherin-11 (CDH11) gene showed the highest frequency of loss (54%, 22 of 41 samples tested). A second hotspot for loss (39%, 9 of 23 samples tested) was detected within intron 2 of the cadherin-13 (CDH13) gene. Furthermore, deletion of the exons of CDH11 and/or WI-5835 was shown by quantitative multiplex PCR in 17 of 30 (57%) of previously untested tumors. Immunoblot analyses revealed that 91% (20 of 22) retinoblastoma exhibited either a complete loss or a decrease of the intact form of CDH11 and 8 of 13 showed a prevalent band suggestive of the variant form. Copy number of WI-5835 for these samples correlated with CDH11 protein expression. CDH11 staining was evident in the inner nuclear layer in early mouse retinal development and in small transgenic murine SV40 large T antigen-induced retinoblastoma tumors, but advanced tumors frequently showed loss of CDH11 expression by reverse transcription-PCR, suggestive of a role for CDH11 in tumor progression or metastasis. CDH13 protein and mRNA were consistently expressed in all human and murine retinoblastoma compared with normal adult human retina. Our analyses implicate CDH11, but not CDH13, as a potential tumor suppressor gene in retinoblastoma.

CDH11 gene copy number and expression are frequently lost in human retinoblastomas and in retinoblastomas arising in TAg-RB mice. To determine the effect of Cdh11 loss in tumorigenesis, we crossed Cdh11 null mice with TAg-RB mice. Loss of Cdh11 had no gross morphological effect on the developing retina of Cdh11 knockout mice, but led to larger retinal volumes in mice crossed with TAg-RB mice (p = 0.01). Mice null for Cdh11 presented with fewer TAg-positive cells at postnatal day 8 (PND8) (p = 0.01) and had fewer multifocal tumors at PND28 (p = 0.016), compared to mice with normal Cdh11 alleles. However, tumor growth was faster in Cdh11-null mice between PND8 and PND84 (p = 0.003). In tumors of Cdh11-null mice, cell death was decreased 5- to 10-fold (p<0.03 for all markers), while proliferation in vivo remained unaffected (p = 0.121). Activated caspase-3 was significantly decreased and beta-catenin expression increased in Cdh11 knockdown experiments in vitro. These data suggest that Cdh11 displays tumor suppressor properties in vivo and in vitro in murine retinoblastoma through promotion of cell death.