Ubiquitin carboxyl-terminal esterase L1 (UCHL1) expression is reduced in retinoblastoma tumor samples

Abstract

Purpose: Ubiquitin carboxyl-terminal esterase L1 (UCHL1) is a deubiquitinase enzyme within the ubiquitin proteasome system that seems to either promote or to block cancer progression in a context dependent manner. UCHL1 is highly expressed in nervous tissue including retina, but there is no data regarding UCHL1 expression or function in retinoblastoma. We used tissue arrays to measure UCHL1 protein expression in human retinoblastoma tumor samples and compared it to normal retina and to other ocular tissues.

Methods: Retinoblastoma tissue arrays were purchased from USBiomax, Inc. Each tissue contained 12 cores of normal ocular tissue (including 4 retinal), and 28 retinoblastoma cores. UCHL1 expression was measured by immunohistochemistry using a rabbit polyclonal antibody against UCHL1 (Abcam), HRP-polymer (TexGen) and DAB (Sigma-Aldrich) as per manufacturer’s guidelines. Two independent observers ranked the area of the tissue stained (S) from 0-100 (0=no staining; 100=all tumor stained) and the intensity of the staining (I) from 0-3 (0=weak; 3= very strong). The quick-score method (Q=SxI) was used to compare UCHL1 expression across the tissue array. T-test analyses were used to determine statistically significant differences in UCHL1 levels (p<0.05).

Results: Low Q-scores (0-60) were obtained for 75% of the non-retinal ocular tissues and for 53% of the tumor samples. Intermediate Q-scores (100<Q<200) were obtained for 25% of the non-retinal ocular tissues and for 32% of the retinoblastoma samples. High Q-scores (Q>200) were obtained for all retinal samples and for 11% of the retinoblastomas. The high levels of UCHL1 detected in retinal samples were statistically significant compared both to non-retinal ocular tissues (p=0.00043) and to retinoblastomas (p=0.004). The observed staining pattern in normal retinal was in agreement with previous reports and concentrated in neuroretinal cells while UCHL1 expression in retinoblastoma seemed to cluster in regions of high mitotic index known as Flexner-Wintersteiner rosettes.

Conclusions: Our data was consistent with a reduced UCHL1 expression in retinoblastoma compared to normal retina. Ongoing experiments using retinoblastoma cell lines as model system will enable us to elucidate potential roles for UCHL1 in retinoblastoma pathogenesis and may also help us find novel molecular targets for retinoblastoma.

Keywords: 703 retinoblastoma • 554 immunohistochemistry