MHC class I antigen processing pathway defects, ras mutations and disease stage in colorectal carcinoma

Abstract

Colorectal tumorigenesis has been associated with the progressive acquisition of a variety of genetic alterations. These include mutations of the Ki-ras proto-oncogene in codons 12 and 13, which account for 85% of genetic changes in colorectal cancer. In murine in vitro models of oncogenic transformation, an association between ras-mediated transformation and downregulation of different components of the MHC class I antigen processing machinery (APM) has been described. In order to investigate whether this association also exists in human tumors, 10 cases of high-grade intraepithelial neoplasia (HIN), as well as primary tumors and autologous lymph node metastases from 42 patients with colorectal carcinoma, were monitored by allele-specific restriction analysis for Ki-ras mutations. In parallel, APM component expression and tumor cell proliferation were analyzed by immunohistochemistry. In comparison to autologous colorectal mucosa, TAP1, LMP2 and tapasin loss was found in 68%, 67% and 80% of HIN, respectively. In contrast, impaired TAP1, LMP2 and tapasin expression was found in 42%, 42% and 63% of primary adenocarcinomas of stage III disease and in 63%, 47% and 79% of the matched lymph node metastases, respectively. More than 60% of colorectal tumor lesions with TAP1, LMP2 and/or tapasin defects displayed Ki-ras mutations. The frequency of TAP1, LMP2 and tapasin loss varied between 33% of primary adenocarcinomas, 40% of HIN to approximately 67% of metastases. These data suggest that i) APM component deficiencies occur more frequently in Ki-ras-mutated colorectal carcinoma lesions and ii) APM abnormalities in conjunction with Ki-ras mutations appear to be associated with disease stage. These findings support the hypothesis that Ki-ras mutations may contribute to immune escape mechanisms of tumors by downregulating the MHC class I APM component expression. © 2003 Wiley-Liss, Inc. Key words: ras; MHC; colorectal cancer; antigen processingImmune responses against tumors are mainly based on the activation of cytotoxic CD8 ϩ T lymphocytes (CTL), which recognize endogenously generated and processed antigenic peptides in the context of MHC class I molecules. The classical MHC class I antigen processing and presentation pathway involves protein degradation mediated by the multimeric proteasome complex, particularly the interferon (IFN)-␥ inducible subunits LMP2, LMP7 and LMP10. 1,2 The yielded peptides are then translocated across the endoplasmic reticulum (ER) membrane via the ATPdependent heterodimeric transporters associated with antigen processing subunits TAP1 and TAP2. [3][4][5] In the ER, the assembly of newly synthesized MHC class I heavy chain (HC) molecules with ␤ 2 -microglobulin (␤ 2 -m) and peptide is assisted by transient interactions with a number of ER-resident chaperones. These include calnexin, calreticulin, protein disulfide isomerase, the thioloxidoreductase ER60 and tapasin. 6 During peptide loading, a multimeric TAP complex is formed that consists of both TAP subunits, the MHC class I antigens, calr...

Loss of tapasin in human lung and colon cancer cells and escape from tumor-associated antigen-specific CTL recognition

“…8,9 Loss of tapasin expression is a frequent event that has been reported in a wide variety of human cancers, including malignant melanoma, head and neck squamous cell carcinoma (HNSCC), renal cell carcinoma, colorectal carcinoma, glioblastoma, lung carcinoma, and neuroblastoma. [10][11][12][13][14][15][16][17][18] Notably, tapasin expression associated with intratumoral T-cell infiltration has been reported as a prognostic marker of patient survival in ovarian carcinoma, HNSCC, glioblastoma, and colorectal carcinoma. 12,13,[19][20][21] It is also reported that loss of tapasin is more frequent among the other antigen-processing machinery (APM) components, strongly suggesting its central role in escape from CTL immune surveillance to tumors.…”

“…12,13,[19][20][21] It is also reported that loss of tapasin is more frequent among the other antigen-processing machinery (APM) components, strongly suggesting its central role in escape from CTL immune surveillance to tumors. 15,22 Impaired CTL responses against tapasin-deficient cells have been well established in mouse models. 8,9 In human cases, loss of tapasin alters the peptide repertoire presented by HLA-B Ã 2705 and results in a decrease in alloreactive CTL responses.…”

Blocking oncogenic RAS enhances tumour cell surface MHC class I expression but does not alter susceptibility to cytotoxic lymphocytes

“…In this case, reduced expression of antigen presentation pathway components restricts the flow of peptide loaded MHC class I molecules to the cell surface [15]. Expression of oncogenic RAS has previously been linked with the reduced expression of antigen presentation pathway components in mouse cells and in human tumour tissue [16][17][18] (and reviewed in [3]). These components include the transporter of antigen processing (TAP) and the TAP-associated molecule, tapasin, which are required for efficient delivery of antigenic peptides into the endoplasmic reticulum (ER) [14].…”

“…This suggests that targeted inactivation of oncogenic RAS may restore expression of MHC class I molecules to the cell surface and help to boost T cell recognition. However, there are conflicting reports on the association between RAS mutations and antigen presentation in human tumours [18][19][20], indicating that functional studies are required. We have analysed the role of mutant RAS oncogenes in regulating the expression of MHC class I molecules and in determining the recognition of RAS mutant tumours by cytotoxic lymphocytes.…”

The mutation in the ATP-binding region of JAK1, identified in human uterine leiomyosarcomas, results in defective interferon-γ inducibility of TAP1 and LMP2

“…Interferon (IFN)-g-inducible genes, for instance the proteasome subunits, low molecular weight proteins (LMP)2, LMP7, LMP10 and the antigen transporters, transporters associated with antigen processing (TAP) 1 and TAP2, appear to be obligatory for the T-cell target recognition of tumors (Driscoll et al, 1993;Gaczynska et al, 1993;Belich et al, 1994;Momburg et al, 1994a, b;Groettrup et al, 1997;Seliger et al, 2000). Many tumor cells unfortunately have lost this ability, thereby evading CTL-mediated immune surveillance and elimination (Garrido et al, 1997;Seliger et al, 2000;Dunn et al, 2002;Miyagi et al, 2003;Atkins et al, 2004). The defective antigen presentation by MHC class I is attributed to the downregulation of several genes required for antigen processing or presentation, such as TAP1 and TAP2, and LMP2 and LMP7 (Singal et al, 1996;Dovhey et al, 2000;Cabrera et al, 2003).…”