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Expression of Bcl-2 in canine osteosarcoma
F. Piro, L. Leonardi "Expression of Bcl-2 in canine osteosarcoma", ISSN: 2218-6050
Abstract
Osteosarcoma (OS) is the most common primary malignancy of bone. It is responsible for 80-85% of the primary bone tumors affecting dogs and it is characterized by aggressive and invasive behavior, with a high metastatic potential. Several studies on cancer and related tumorigenesis, show an involvement of the mechanisms of programmed cell death and cell survival. Many signals seem to be involved in the related mechanism of autophagy and in particular, our interest is focused on the expression of a family of Bcl-2 that seems to be involved either in the control of biomolecular mechanisms like autophagy and apoptosis. In this study we investigated the expression of Bcl-2 in different cases of spontaneous canine osteosarcoma and the related preliminary results are described. We found Bcl-2 activity was increased in OS tissue compared to normal bone tissue. These results suggested that Bcl-2 activity may play an important role in the formation of OS and as a diagnostic for neoplastic activity. However, further research is needed to confirm the role of Bcl-2 activity in OS in canines.
Introduction
Osteosarcoma (OS) is the most common primary malignancy of the skeleton of dogs and humans. OS arises most commonly in the metaphyseal region of long bones, within the medullary cavity,
and penetrates the cortex of the bone to involve the surrounding soft tissues (Broadhead et al., 2011).In dogs OS represents 80 to 85% of bone tumors, most frequently affecting male dogs
of medium to large breeds between 2-years and 12-years of age (Leonardi, 2003 and Leonardi et al., 2014). In dogs 24% of OS typically affects the axial skeleton, while the
involvement of the appendicular skeleton is rather high (> 70% of cases) (Liu et al., 1977). Here we
investigated immunohistochemically the expression of Bcl-2, an important membrane protein involved in
apoptotic/autophagic mechanisms and expressed in several premalignant and malignant lesions and which
its role is still not clarified in spontaneous osteosarcoma (Leoncini et al., 1993). Apoptosis is the
so-called programmed cell death that occurs when the damaged cell is no longer able to activate the repair
systems (Stergiou and Hengartner, 2004). This mechanism can be triggered by external stimuli such
as chemical or physical agents, or endogenous stimuli such as cell turnover or remodelling during cellular
development.
In tumor formation, apoptosis is usually inhibited and the cells involved undergo uncontrolled proliferation
(Robert et al., 2012) Autophagy is an evolutionarily conserved process that involves cellular self-eating
(Mizushima et al., 2008). This mechanism of stress adaptation and degrading acts of cytoplasmic contents, it is in fact physiologically activated under conditions of nutrient deficiency.
The process is based on the
formation of a vesicles which takes the name of autophagosome, capable of sequestering damaged and
degraded cytoplasmic organelles (Brech et al., 2009). The tumor suppressor function operated by autophagy
is mediated by scavenging of damaged oxidative organelles, thus preventing accumulation of toxic
oxygen radicals that would cause the genome instability. However, in some cases autophagy can
also promote the survival of cancer cells once tumors have developed. This is attributed to the ability of
autophagy to promote cell survival under conditions of poor nutrient supply, as often faced by solid tumors
and metastasizing cancer cells (Brech et al., 2009).
Research works conducted on the study of the mechanism of autophagy in tumors has led to
identifying the involvement of a family of proteins that are also involved in apoptosis mechanisms. This
family of protein is called Bcl-2 and is localized on the outer mitochondrial membrane, already involved
in the apoptotic mechanism (Levine et al., 2008). They are part of a family of more than 15 different
proteins that are grouped into two categories according to which play a role in pro-apoptotic or anti-
apoptotic cells. The same differentiation was found in the autophagic mechanism, In fact it has been
demonstrated that the anti-apoptotic proteins Bcl-2 and Bcl-X1 also have the ability to inhibit autophagy
through binding to a specific domain, which takes the name of BH3, present on a protein known with the
name of Beclin1 involved in the regulation of autophagy (Robert et al., 2012). In humans it was identified that autophagy had an important role in the development of bone cancer (Huang et
al., 2012) and might be interesting to investigate whether this mechanism, involved in the process that affects the human being, is equally involved in OS in canines.The aim of this
preliminary study was to evaluate the immunohistochemical expression of Bcl-2 in
spontaneous canine osteosarcoma being known its role in cell proliferation and tumorigenesis.
Materials and Methods
Ten cases of spontaneous high grade canine osteoblastic non metastatic osteosarcoma have been
used to investigate the immunohistochemical expression of Bcl-2 through the use of specific
antibody. The biological samples was represented by tumors resection pieces from patients hospitalized in
different Clinics in Italy.
Tumor’s samples were fixed in 10% neutral buffered formalin and subsequently were subjected to
decalcification for bone tissues composed by an aqueous solution of formic acid, hydrochloric and
sulphuric acid in different parts, left at room temperature for a variable time in relation to the
degree of daily decalcification. Samples were then processed using common histopathological techniques
and stained with Hematoxylin and Eosin (H&E) stains were performed on 3-5μ sections. The
histopathological diagnoses were done in conformity with criterions established in 1994 by WHO
classification of bone tumors (Slayter et al., 1994) (Table 1).
Table 1. Clinical data of samples used for IHC investigation.
Immunohistochemistry (IHC) was performed using the Avidin Biotin Complex (ABCL-2) method
(Abcam kit). Paraffin was removed with xylene and slides were dehydrated in sequential diluted ethanol
and then rinsed in distilled water. To inhibit endogenous peroxidase activity the tissue sections
were treated with 3% hydrogen peroxide in tris phosphate-buffered saline (PBS). Non-specific
reactivity was blocked with the use of normal goat serum for 30 minutes. Investigations was performed
on serial sections of 3-5 μm using monoclonal antibody mouse antihuman Bcl-2 (clone 124, dilution
1:100, Dako). Samples of normal canine tonsil were used as a positive control for Bcl-2.
Results
Histologically, all tumors were highly cellular with polyhedral cells with large nuclei and hypercromatic
chromatin, frequent mitoses and prominent nucleoli associated with production of different amount of
osteoid. Bcl-2 immunostaining showed homogeneous increasing expression in all cases investigated,
compared with normal bone in all samples investigated (Fig.1).
The percentage of immunohistochemically positive cells in all cases investigated ranged from 80% to
95%. Fluorescence was always in the cytoplasm, consistent with normal mitochondrial membrane
activity.
Fig. 1. Bcl-2 expression in spontaneous canine osteoblastic osteosarcoma. Bcl-2 is expressed with prevalent cytoplasmic immunoreactivity by tumoral osteoblastic cells that appears in agglomerated well packed group of cells throughout the lamellar bone structures negative for Bcl-2 IHC as well as the upper isle of cartilage. IHC magnification x20.
Discussion
Bcl-2 is a protein belonging to a family that regulates different mechanisms of cell biology like autophagy
and apoptosis (Yip and Reed, 2008). Bcl-2 is an anti- apoptotic protein that may protect cells from a variety
of apoptotic stimuli, including cytotoxic drugs, irradiation, heat or growth factor withdrawal (Creagh
et al., 2000). The over expression of Bcl-2 has been described in different types of human tumors,
including breast, colon, ovary and prostate cancers (Amundson et al., 2000).
Although Bcl-2 confers resistance to malignant cells, it does not always correlate with poor prognosis
(Hassan et al., 2014). Our results showed an over expression of Bcl-2 in all tumoral osteoblastic cells
from all primitive canine osteosarcoma investigated. This positive expression suggest that is possible to
speculate the inhibition of the mechanism of programmed cell death in according with the
neoplastic event. The results obtained during this preliminary study may suggest that the assessment of
the degree of expression of Bcl-2 may play an important role in diagnosing neoplastic event but the
role of Bcl-2 as a prognostic marker have to be still investigate.
The over expression of Bcl-2 protein in osteosarcoma samples suggests that also alterations of mechanisms
of autophagy/apoptosis may have a role in the bone tumor formation, and suggest too that the Bcl-2
protein during the neoplastic process may loss natural action of anti-apoptotic protein that consequently
contribute to stimulate the uncontrolled proliferation of tumor cells.
These results suggest that Bcl-2 protein could work first as anti-apoptotic factor that may prepossess
proliferative index activity of osteosarcoma and therefore its aggressiveness. We believe that
evaluation of Bcl-2 expression may be used as a diagnostic co-marker but its role as a prognostic
marker needs to be further investigate. In conclusion this preliminary study reveals that osteoblastic
osteosarcoma provide evidence for Bcl-2 expression that suggesting an involvement of this protein in
development of this tumor.
Acknowledgments
The authors gratefully acknowledge support from the “Centro Funzionale di Patologia Veterinaria per il
Registro dei Tumori Animali della Regione Umbria” and to Dr. Emilia Del Rossi, from Department of
Veterinary Pathology in Perugia – Italy, and to Ms. Jennifer A. Safko and Ms. Chaterine Teresa Malehorn
from Athens - Georgia (USA) for their help.
Conflict of interest
The authors declares that there is no conflict of interest.
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