A comparison of ocular melanocyte and uveal melanoma cell invasion and the implication of α1β1, α4β1 and α6β1 integrins

Abstract

Background/aims-Posterior uveal melanoma is the most common intraocular tumour in adults, responsible for the death of approximately 35% of patients. Hepatic metastases are most frequent, and once diagnosed survival is usually less than 1 year. The 1 family of integrins, v 3 and MMP-2 and MMP-9 have been implicated in the metastasis of several types of tumour. To study their involvement in uveal melanoma we analysed the expression of the 1 integrins, v 3, MMP-2, and MMP-9 in 10 primary posterior uveal melanomas, and correlated expression with invasive potential in vitro. Comparable studies were undertaken on cultures of melanocytes. Methods-Expression of integrins was studied by immunohistochemistry, secretion of MMP-2 and MMP-9 by zymography, and the invasive potential was assessed using a transwell model. Results-MMP-2 was secreted by all uveal melanomas and seven of 10 secreted MMP-9. Among uveal melanoma, invasion levels of 4-25% were observed and the major integrins expressed were 1 1, 2 1, 3 1, 5 1, and av 3. Melanocytes did not express 1 1, 4 1, and 6 1. Conclusion-The laminin binding 6 1 integrin was not expressed by either melanocytes or tumours with spindle morphology, which are considered to have a better prognosis. It is possible that expression of the 6 1 integrin may prove useful as a prognostic indicator. (Br J Ophthalmol 2001;85:732-738) Posterior uveal melanoma is the most common primary intraocular tumour in adults.1 Despite new methods of treating the primary melanoma, the survival rate has remained unchanged because of the problem of detection and treatment of metastases.2 Unlike cutaneous melanoma, which metastasises via lymphatic or haematogenous routes to various sites, uveal melanoma mainly disseminates haematogenously and preferentially establishes secondary disease in the liver.3 At least 30% of patients will develop metastases within 10 years of successful treatment of the primary tumour, 4 but at initial presentation, only 1-2% of patients show evidence of hepatic involvement.5 Detection of liver micrometastases is diYcult with currently available clinical tests and it is thought that many patients have subclinical metastases at diagnosis.5 Once metastatic disease has been detected, survival is usually less than 1 year.2 6 Traditional prognostic indicators are based on assessment of the diameter and histological appearance of the tumour 7 8 but it remains diYcult to determine which patients at initial presentation are at high risk of developing metastases.Metastasis is a "multistep" process and tumour cells are required to invade through extracellular matrices (ECMs) at various times during the process. It is proposed that a number of cells detach from the primary tumour and attach via adhesion molecules to components of the ECM or vascular endothelium to be invaded.9 ECM proteins are then degraded by proteolytic enzymes released from the primary tumour or the surrounding stroma.

Invasive and noninvasive uveal melanomas have different adhesive properties

“…13 In this present study, a similar pattern of a1-and a4-expression was observed between invasive and noninvasive cells (Table 2), while lower levels of a6-expression were detected on noninvasive cells when compared with their invasive counterparts (Table 2). Together, these data support an involvement of these receptors with malignant progression and the invasive phenotype previously demonstrated.…”

“…Expression of ICAM-1 has been associated with an increased risk of uveal melanoma metastasis 15 and worse prognosis in cutaneous melanoma, 4,32 and similarly invasive cells studied here expressed higher levels than their noninvasive counterparts (Table 2), also implicating an involvement of ICAM-1 in invasion. As described previously, both uveal melanocytes 13 and noninvasive cells do not express a4-integrins, while increased levels were detected on invasive cells (Table 2). Although little is known about a4-integrins and uveal melanoma metastasis, ligation of a4b1 with its endothelial ligand VCAM-1 is involved with cutaneous melanoma metastasis, 7 and the pattern of spread is proposed to relate to organ-specific VCAM-1 expression.…”

“…Together, these data support an involvement of these receptors with malignant progression and the invasive phenotype previously demonstrated. 6,13,17 In this current study, inclusion of blocking antibodies in ECM adhesion assays identified that a1-and a6-integrins on SOM 196B cells are involved with attachment to collagens I and IV and laminin (Table 2), with these cells correspondingly adhering at higher levels to these substrates than noninvasive SOM 157d (Figure 1). As both laminin and collagen type IV are found in high levels in the BM, and premetastatic uveal melanoma cells, associated with a better prognosis, lack laminin receptors, 21 this would similarly infer an involvement of a1-and a6-integrins with uveal melanoma invasion.…”

“…The highly significant difference (Po0.001) in numbers of invasive and noninvasive cells attaching to the endothelium would suggest that adhesion to the vasculature is vital in determining the invasive phenotype. The absence of a1-and a4-integrins on noninvasive cells and uveal melanocytes, 13 mediating the adhesive interactions studied, would infer a vital role for these receptors in uveal melanoma invasion. Further investigation into the factors regulating these interactions is required to improve an understanding of uveal melanoma metastasis.…”

“…In particular, while cutaneous melanomas metastasise widely, uveal melanomas commonly spread to the liver and other sites are less frequently affected. Uveal melanomas are reported to express a range of adhesion molecules, including integrins, and members of the immunoglobulin family members, 6,[12][13][14][15] but only the expression of intercellular cellular molecule-1 (ICAM-1) has so far been shown to bear any relationship to clinical outcome. 15 Little is, however, known about how adhesion molecule expression in uveal melanomas may influence the invasion process, and it is unclear whether the same mechanisms important in cutaneous melanoma are equally relevant, or if different interactions are required.…”