Smooth muscle myosin phosphatase dephosphorylates the regulatory myosin light chain and thus mediates smooth muscle relaxation. The activity of this myosin phosphatase is dependent upon its myosin-targeting subunit (MYPT1). Isoforms of MYPT1 have been identified, but how they are generated and their relationship to smooth muscle phenotypes is not clear. Cloning of the middle section of chicken and rat MYPT1 genes revealed that each gene gave rise to isoforms by cassette-type alternative splicing of exons. In chicken, a 123-nucleotide exon was included or excluded from the mature mRNA, whereas in rat two exons immediately downstream were alternative. MYPT1 isoforms lacking the alternative exon were only detected in mature chicken smooth muscle tissues that display phasic contractile properties, but the isoform ratios were variable. The patterns of expression of rat MYPT1 mRNA isoforms were more complex, with three major and two minor isoforms present in all smooth muscle tissues at varying stoichiometries. Isoform switching was identified in the developing chicken gizzard, in which the exon-skipped isoform replaced the exon-included isoform around the time of hatching. This isoform switch occurred after transitions in myosin heavy chain and myosin light chain (MLC(17)) isoforms and correlated with a severalfold increase in the rate of relaxation. The developmental switch of MYPT1 isoforms is a good model for determining the mechanisms and significance of alternative splicing in smooth muscle.

Bone is one of the most common sites of cancer metastasis in humans and is a significant source of morbidity and mortality. Bone metastases are considered incurable and result in pain, pathologic fracture, and decreased quality of life. Animal models of skeletal metastases are essential to improve the understanding of the molecular pathways of cancer metastasis and growth in bone and to develop new therapies to inhibit and prevent bone metastases. The ideal animal model should be clinically relevant, reproducible, and representative of human disease. Currently, an ideal model does not exist; however, understanding the strengths and weaknesses of the available models will lead to proper study design and successful cancer research. This review provides an overview of the current in vivo animal models used in the study of skeletal metastases or local tumor invasion into bone and focuses on mammary and prostate cancer, lymphoma, multiple myeloma, head and neck squamous cell carcinoma, and miscellaneous tumors that metastasize to bone.

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Abstract-In rodents, angiotensin (Ang) II type-1 (AT1) receptors exist as two pharmacologically identical subtypes: AT1a and AT1b. Recent studies have utilized mouse models with specific subtype receptor deletions to differentiate the functional difference between AT1 subtypes. However, little information is available on AT1 subtype expression in mouse vasculature. Therefore, in this study, AT1a Ϫ/Ϫ mice and wild-type littermates (AT1a ϩ/ϩ ) were used to examine AT1 subtype expression and its functional relevance in mouse arterial vessels. Using RT-PCR and restriction enzyme digestion, we showed that AT1b accounts for most of the total AT1 mRNA in mouse abdominal aorta and femoral artery. In contrast, AT1a is the predominant subtype in kidney. To study the functional role of AT1 subtypes, we measured the in vitro contractility in vessels from AT1a Ϫ/Ϫ and AT1a ϩ/ϩ mice. The Ang II concentration response curves in abdominal aorta and femoral artery were comparable between the two mouse strains. Furthermore, the Ang II response in AT1a Ϫ/Ϫ mouse vessels was completely antagonized by losartan, an AT1 antagonist. These results demonstrate that AT1b receptor is a major mediator for Ang II contractile response in mouse vessels, such as abdominal aorta and femoral artery.

Genetically altered mice are increasingly used as experimental models. However, ANG II responses in mouse blood vessels have not been well defined. Therefore, the aim of this study was to determine the role of ANG II in regulating major blood vessels in C57/BL6J mice with isometric force measurements. Our results showed that in mouse abdominal aorta ANG II induced a concentration-dependent contraction (EC50 4.6 nM) with a maximum contraction of 75.1 +/- 4.9% at 100 nM compared with that of 60 mM K+. Similarly, femoral artery also exhibited a contractile response of 76.0 +/- 3.4% to the maximum concentration of ANG II (100 nM). In contrast, ANG II (100 nM)-induced contraction was significantly less in carotid artery (24.5 +/- 6.6%) and only minimal (3.5 +/- 0.31%) in thoracic aorta. The nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester and the AT2 antagonist PD-123319 failed to enhance ANG II-induced contractions. However, an AT1 antagonist, losartan (10 microM), completely inhibited ANG II (100 nM) response in abdominal aorta and carotid artery. An AT1 agonist, [Sar1]-ANG II (100 nM), behaved similarly to ANG II (100 nM) in abdominal aorta and carotid artery. RT-PCR analyses showed that mouse thoracic aorta has a significantly lower AT1 mRNA level than abdominal aorta. These results demonstrate that major mouse vessels exhibit differential contractions to ANG II, possibly because of varied AT1 receptor levels.

Objectives Oral squamous cell carcinoma (OSCC) is the most commonly diagnosed oral malignancy in humans and cats and frequently invades bone. The objective of this study was to determine if feline OSCC serves as a relevant model of human OSCC in terms of osteolytic behavior and expression of bone resorption agonists. Materials and Methods Novel feline OSCC cell lines (SCCF2 and SCCF3) were derived from spontaneous carcinomas. Gene expression and osteolytic behavior were compared to an established feline OSCC cell line (SCCF1) and three human OSCC cell lines (UMSCC-12, A253 and SCC25). Interaction of OSCC with bone and murine pre-osteoblasts (MC3T3) was investigated using in vitro co-culture techniques. In vivo bioluminescent imaging, faxitron radiography and microscopy were used to measure xenograft growth and bone invasion in nude mice. Results Human and feline OSCC expressing the highest levels of parathyroid hormone-related protein (PTHrP) were associated with in vitro and in vivo bone resorption and osteoclastogenesis. MC3T3 cells had increased receptor activator of nuclear factor κB ligand (RANKL) expression and reduced osteoprotegerin (OPG) expression in conditioned medium from bone-invasive SCCF2 cells compared to minimally bone invasive SCCF3 cells, which was partially reversed with a neutralizing anti-PTHrP antibody. Human and feline OSCC cells cultured in bone-conditioned medium had increased PTHrP secretion and proliferation. Conclusion Feline OSCC-induced bone resorption was associated with tumor cell secretion of PTHrP and with increased RANKL : OPG expression ratio in mouse preosteoblasts. Bone-CM increased OSCC proliferation and secretion of PTHrP. The preclinical models of feline OSCC recapitulated the bone-invasive phenotype characteristic of spontaneous OSCC and will be useful to future preclinical and mechanistic studies of bone invasive behavior.

The findings of the present study demonstrate that expression of mutant CASQ2(D307H) in the mouse heart results in abnormal myocyte Ca2+ handling and predisposes to complex ventricular arrhythmias similar to the CPVT phenotype observed in human patients.

Adult T-cell leukemia/lymphoma (ATLL) is caused by human T lymphotropic virus type 1 (HTLV-1). Patients with ATLL frequently develop humoral hypercalcemia of malignancy (HHM) resulting from increased osteoclastic bone resorption. Our goal was to investigate the mechanisms of ATLL-induced osteoclastic bone resorption. Murine calvaria co-cultured with HTLV-1-infected cells directly or conditioned media from cell cultures had increased osteoclast activity that was dependent on RANKL, indicating that factors secreted from ATLL cells had a stimulatory effect on bone resorption. Factors released from resorbing bone stimulated proliferation of HTLV-1-infected T-cells. Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1α (MIP-1α), both osteoclast stimulators, were expressed in HTLV-1-infected T-cell lines. Interestingly, when HTLV-1-infected T-cells were co-cultured with pre-osteoblasts, the expression of osteoprotegerin (OPG), an osteoclast inhibitory factor, was significantly down-regulated in the pre-osteoblasts. When OPG was added into the ex vivo osteoclastogenesis assay induced by HTLV-1-infected T-cells, osteoclastogenesis was strongly inhibited. In addition, HTLV-1-infected T-cells inhibited expression of early osteoblast genes and induced late genes. These regulators will serve as future therapeutic targets for the treatments of HHM in ATLL.