Mice heterozygous for a mutation at the Nf2 tumor suppressor locus develop a range of highly metastatic tumors

Abstract

A role for the membrane/cytoskeleton interface in the development and progression of cancer is established, yet poorly understood. The neurofibromatosis type II (NF2) tumor suppressor gene encodes a member of the ezrin/radixin/moesin (ERM) family of membrane/cytoskeleton linker proteins thought to be important for cell adhesion and motility. We report that in contrast to the narrow spectrum of benign tumors in human NF2 patients, Nf2 heterozygous mice develop a variety of malignant tumors. Using the fact that Nf2 is linked to the p53 tumor suppressor locus in the mouse we have also investigated the effects of genetic linkage of cancer-predisposing mutations on tumorigenesis and examined the genetic pathway to tumor formation involving Nf2 loss. Importantly, we observed a very high rate of metastasis associated with Nf2 deficiency, with or without loss of p53 function, and we provide experimental evidence supporting a role for Nf2 loss in metastatic potential. Together, our results suggest an important role for the NF2 tumor suppressor, and perhaps the ERM family in tumor formation and metastasis.[Key Words: Merlin; NF2; tumor suppressor; cytoskeleton; osteosarcoma; metastasis]Received January 20, 1998; revised version accepted February 25, 1998. Neurofibromatosis type II (NF2) is a dominantly inherited disorder featuring the predisposition to develop multiple benign tumors of the central nervous system. The hallmark feature of NF2 is the development of bilateral schwannomas of the eighth cranial (auditory) nerves; NF2 patients are also predisposed to the development of spinal schwannomas, meningiomas, and ependymomas at rates much higher than that of the normal population (Huson 1994). The NF2 tumor suppressor gene was identified by positional cloning and loss of heterozygosity (LOH) studies and found to encode a member of the band 4.1 family of cytoskeletal-associated proteins thought to be involved in the organization of the actin cytoskeleton (Rouleau et al. 1993;Trofatter et al. 1993). The NF2 gene product shares closest similarity to ezrin, radixin, and moesin (the ERM proteins), which comprise a subset of this family, and thus was given the name merlin (moesin-, ezrin-, and radixin-like protein) (Trofatter et al. 1993). The amino-terminal halves of these proteins share the greatest similarity (the band 4.1 domain), with ∼85% amino acid identity among the ERMs (for review, see Tsukita et al. 1997;Vaheri et al. 1997).The ERM proteins localize to cortical actin structures, particularly specialized or dynamic regions, such as membrane ruffles, microvilli, or the cleavage furrow and can bind directly to actin through a highly conserved motif at their extreme carboxyl terminus (for review, see Tsukita et al. 1997;Vaheri et al. 1997). The ERM proteins may be rendered inactive by an intramolecular association; certain stimuli such as phosphorylation or phosphatidyl-4,5-bis-phosphate (PIP2) binding may serve to ''open up'' the protein conformation, allowing homoor heterodimerization, which has been shown to occu...

Re-expression of the tumor suppressor NF2/merlin inhibits invasiveness in mesothelioma cells and negatively regulates FAK

“…Furthermore, overexpression of merlin has been shown to inhibit motility and spreading in rat Schwannoma cells (Gutmann et al, 1999). Moreover, Nf2( þ /À) mice exhibit a wide range of highly invasive and metastatic tumors (McClatchey et al, 1998). Finally, Nf2( þ /À) mice exposed to asbestos exhibit accelerated formation of highly malignant mesothelial tumors (Fleury-Feith et al, 2003;Altomare et al, 2005).…”

“…Other evidence in support of a possible role of merlin in tumor invasion comes from studies of Nf2-knockout animal models. Although Nf2-null mice die during embryonic development, mice heterozygous for a mutation at the Nf2 locus develop a range of highly invasive and metastatic tumors (McClatchey et al, 1998). Moreover, Nf2 ( þ /À) mice are more susceptible to the MM development after exposure to asbestos than their wild-type counterparts (Fleury-Feith et al, 2003;Altomare et al, 2005).…”

Inhibition of the hyaluronan-CD44 interaction by merlin contributes to the tumor-suppressor activity of merlin

“…Unlike the ERM proteins, merlin lacks the conventional actin-binding region in its COOH-terminus, but it contains an actin-binding site in its NH 2 -terminal domain and interacts indirectly with the actin cytoskeleton through the actin-binding protein, bII-spectrin (Scoles et al, 1998). Association of merlin with the actin cytoskeleton is thought to underlie its effects on actin cytoskeletal organization (Gutmann et al, 1999b), cell spreading (Pelton et al, 1998) and motility (McClatchey et al, 1998). The ERM proteins and merlin likely play different or even opposite roles in organization of the cortical actin and tumorigenesis by differentially affecting the functions of their common binding partners such as CD44.…”

“…CD44 and ezrin play important roles in promoting tumor metastasis (Yu et al, 1997;Stamenkovic 1999, 2000;Yu et al, 2004;Khanna et al, 2001Khanna et al, , 2004, whereas merlin acts as a tumor suppressor (Rouleau et al, 1993;Trofatter et al, 1993;Lutchman and Rouleau, 1995;Sherman et al, 1997;McClatchey et al, 1998;Giovannini et al, 1999Giovannini et al, , 2000. Thus far, the functional relationship between CD44 and merlin and the manner in which CD44 affects the tumor-suppressing activity of merlin have not been established.…”

Modeling metastasis in the mouse

“…The use of transgenic and knockout technology has presented a couple of notable exceptions to this rule (i.e. Guy et al, 1992;McClatchey et al, 1998); the study of these animals and expanded use of genetic manipulation of the mouse genome will undoubtedly have a tremendous impact on our ability to model and study metastasis in vivo in the mouse.…”