Disease relevance of ALK

• Unscheduled expression of the truncated ALK may contribute to malignant transformation in these lymphomas [1].
• Fusion of a kinase gene, ALK, to a nucleolar protein gene, NPM, in non-Hodgkin's lymphoma [1].
• Anaplastic large cell lymphoma (ALCL) is associated with the t(2;5)(p23;q35), which generates the NPM-ALK fusion gene encoding an 80-kD protein [2].
• Occasional non-ALCL B cell lymphomas (4%) with diffuse large cell and immunoblastic histology and Hodgkin's disease cases (3%) were NPM-ALK-, but these data are questionable [3].
• We report a case showing a restricted cytoplasmic staining pattern of ALK and a novel chromosomal abnormality, t(2;22)(p23;q11.2), demonstrated by fluorescence in situ hybridization analysis [4].

High impact information on ALK

• Fusion of a kinase gene, ALK, to a nucleolar protein gene, NPM, in non-Hodgkin's lymphoma [5].
• Expressed in the small intestine, testis, and brain but not in normal lymphoid cells, ALK shows greatest sequence similarity to the insulin receptor subfamily of kinases [1].
• We have identified a highly potent and selective small-molecule ALK inhibitor, NVP-TAE684, which blocked the growth of ALCL-derived and ALK-dependent cell lines with IC(50) values between 2 and 10 nM [6].
• NPM/ALK, in turn, induces the phenotype through activation of its key signal transmitter, signal transducer and activator of transcription 3 (STAT3) [7].
• The anaplastic lymphoma kinase (ALK) on 2p23 is a tyrosine kinase that forms chimeric fusions with numerous translocation partners [8].

Chemical compound and disease context of ALK

• Anaplastic lymphoma kinase (ALK)-positive lymphomas are characterized by expression of a hybrid protein, comprising the cytoplasmic portion of the ALK tyrosine kinase fused to a partner protein [9].
• As STAT3 activation is pathogenetically important in anaplastic lymphoma kinase-positive anaplastic large cell lymphoma (ALK+ ALCL), we investigated whether JSI-124 can mediate significant inhibitory effects in this cell type [10].
• Antibodies detecting hypoglycosylated MUC1 were found to be absent in all lymphomas (SM3) or present in only six of 15 ALK positive ALCLs (VU-4H5) [11].
• To clarify this issue and its epidemiological characteristics, we examined 37 formalin-fixed, paraffin-embedded specimens of CD30+ lymphomas from the United States and Hong Kong by reverse transcriptase-polymerase chain reaction (RT-PCR) for the status of the NPM and ALK genes, which are typically juxtaposed by the t(2;5) translocation [12].
• Whilst the strong labelling for phosphotyrosine observed in the lymphoma cells is due to the presence of activated ALK, the strong staining of some normal cells presumably represents physiologically active kinases and this should be taken into account when interpreting the immunostaining of non-lymphoid tumours [13].

Biological context of ALK

• These findings identify a mechanism of NPM/ALK-mediated oncogenesis based on induction of the Treg phenotype of the transformed CD4(+) T cells [7].
• Flow cytometric analysis revealed that wortmannin-treated NPM-ALK-transformed cell lines underwent apoptosis [14].
• All such cases result from a novel fusion created by the ALK gene on chromosome 2p23 and NPM on 5q35 or other variant translocation partners [15].
• Down-regulation of Bcl-XL significantly reduced the antiapoptotic potential of NPM/ALK in both transformed murine Ba/F3 pro-B cells and human ALCL-derived KARPAS-299 cells [16].
• NPM/ALK kinase activity was required to promote Bcl-XL expression and its protective effect on mitochondrial homeostasis [16].

Anatomical context of ALK

• A rare variant of diffuse large B-cell lymphoma (DLBCL), originally described in 1997, was thought to overexpress full-length ALK in contrast to a chimeric protein characteristic of ALCL [15].
• In agreement, Src-kinase inhibitors or pp60(c-src) siRNA significantly decreased the proliferation rate of NPM-ALK-positive ALCL cell lines [17].
• The CLTCL gene is constitutively expressed in lymphoid cells and therefore presumably contributes an active promoter for the CLTCL-ALK gene [9].
• Primary murine bone marrow retrovirally transduced with NPM-ALK showed a transformed phenotype that was reversible on treatment with PI 3-kinase inhibitors [14].
• The distinctive granular cytoplasmic staining pattern for ALK was likely to be due to binding of the fusion protein to clathrin-coated vesicles [9].

Associations of ALK with chemical compounds

• However, full-length ALK protein lacks tyrosine kinase activity and thus the mechanism of oncogenesis has remained elusive [15].
• We have studied the effect of 17-allylamino,17-demethoxygeldanamycin (17-AAG), a benzoquinone ansamycin, on NPM-ALK steady-state level in ALCL cells [18].
• Previously, nucleophosmin-ALK has been shown to activate phosphatidylinositol 3-kinase (PI3K) and its downstream effector, the serine/threonine kinase AKT [19].
• To study the early consequences of ectopic ALK activation, a GyrB-ALK fusion was constructed that allowed regulated dimerization with the addition of coumermycin [20].
• Our data support that JSI-124 is a potentially useful therapeutic agent for ALK+ ALCL [10].

Physical interactions of ALK

• We describe 6 cases of ALK+ DLBCL characterized by a simple or complex t(2;17)(p23;q23) involving the clathrin gene (CLTC) at chromosome band 17q23 and the ALK gene at chromosome band 2p23 [15].
• Sedimentation gradient experiments revealed that NPM-ALK forms in vivo multimeric complexes of approximately 200 kDa or greater that also contain normal NPM [21].

Regulatory relationships of ALK

• Using cDNA microarrays, ALK(+) ALCL cell lines consistently expressed the highest TIMP1 level among 29 lymphoma cell lines of various subtypes [22].
• We show here that expression of activated ALK induces the constitutive phosphorylation of Stat3 in transfected cells as well as in primary human ALCLs [23].
• Inhibition of JAK3 induces apoptosis and decreases anaplastic lymphoma kinase activity in anaplastic large cell lymphoma [24].
• Using a cDNA microarray, we found that suppressor of cytokine signaling 3 (SOCS3) is highly expressed in anaplastic lymphoma kinase (ALK)+ anaplastic large cell lymphoma (ALCL) cell lines [25].
• The present cases of ALCL associated with a novel t(1;2)(q25;p23) demonstrate that at least one fusion partner other than NPM can activate the intracytoplasmic domain of the ALK kinase [26].

Other interactions of ALK

• Moreover, these results demonstrate the presence of CLTC-ALK fusions in these tumors and extend the list of diseases associated with this genetic abnormality to include classical T-cell or null ALCL, ALK+ DLBCL, and inflammatory myofibroblastic tumors [15].
• A new fusion gene TPM3-ALK in anaplastic large cell lymphoma created by a (1;2)(q25;p23) translocation [26].
• Here we have identified TRK-fused gene (TFG) as a new ALK partner in 2 ALCL, 1 of which exhibited a t(2;3)(p23;q21) [2].
• In conclusion, STAT3 directly contributes to the high level of TIMP1 expression in ALK(+) ALCL, and TIMP1 expression correlates with high level of STAT3 activation in ALCL [22].
• Other rearrangements involving the ALK gene have recently been shown to be associated with ALCL, among which the ATIC-ALK rearrangement resulting from the inv(2)(p23q35) translocation is probably the most recurrent [27].

Analytical, diagnostic and therapeutic context of ALK

• Using a polymerase chain reaction (PCR)-based technique to walk on chromosome 2 from the known ALK gene across the breakpoint, we showed that the gene involved at 1q25 is TPM3, encoding a nonmuscular tropomyosin [26].
• These results were further validated in fibroblastic NIH-3T3 cells expressing a previously described chimeric epidermal growth factor receptor (EGFR)/ALK molecule that allows dissection of ALK enzymatic function under conditions of controlled ligand-induced activation [28].
• Results of the RT-PCR were compared to ALK immunostaining, cytogenetics, and fluorescence in situ hybridization (FISH) results [27].
• We further evaluated the relationship between TIMP1 expression and STAT3 activation in 43 ALCL tumors (19 ALK(+) and 24 ALK(-)) using immunohistochemistry and a tissue microarray [22].
• Here, we show molecular cloning of cDNAs for both the human and mouse ALK proteins [29].

References