**5. Final remarks**

be considered is the fact that viral integration into the host genome frequently leads to loss of E1/E2 gene expression, meaning that established cancers are likely to have lost the molecules

In contrast, E6 and E7 are frequently over-expressed in established cancers, making these two proteins quite attractive as targets. E6 and E7 are the zinc finger-containing proteins primarily responsible for the malignant alterations and de-differentiation of keratinocytes observed during cell transformation. These changes occur following integration of the HPV genome into host DNA [163, 176]. During this process, the regulators of viral replication, E1 and E2, are frequently disrupted, allowing over-expression of E6 and E7. HR-HPV types induce cell immortalization and transformation primarily through the over-expression of E6 and/or E7, which are best known for their ability to accelerate the degradation of the p53 and retinoblas‐ toma proteins (pRB), respectively. The E6-mediated loss of p53 function leads to an insensi‐ tivity to apoptotic signals as well as to a loss of cell cycle regulation at the G1/S checkpoint in response to DNA damage. E7 contributes to the hyperplasia crisis by accelerating the degra‐ dation of pRB and thereby stimulating cells in Interphase to re-enter the cell cycle at S phase [177-179]. Together, over-expression of the E6 and E7 oncoproteins, decrease apoptosis and increase cell division, setting the stage for cancer [180]. Antiviral agents that can partially, if not fully, inhibit E6 and/or E7 functions clearly have the potential to negatively impact the carcinogenic process. One group, for example, proposed such a strategy in their study of the HPV16 E7-antagonizing peptide, Pep-7 [181]. Pep-7 was originally introduced as a short peptide component of the vacuole/lysosomal pathway [182]. However, Pep-7 was later shown not only to reduce the viability of HPV-positive cells *in vitro*, but it also decreased expression of E7 in SiHa cells in a xenograft model. It is conjectured that the selective mechanism Pep-7 uses to suppress cell proliferation may hinge on its ability to obstruct E7-pRB associations,

In contrast to E7, which appears to act primarily by increasing the ability of expressing cells to replicate, E6 acts by reducing the ability of expressing cells to undergo apoptosis. Apoptosis is a natural, cell-mediated death response to irreparable DNA damage. One target of E6 is the p53 tumor suppressor, which is degraded following association of E6 with the ubiquitin protein ligase, E6AP. The E6/E6AP complex binds to p53 and initiates its ubiquitination and conse‐ quent proteolytic destruction [183]. This means that the downstream targets of p53, which mediate cell cycle arrest and apoptosis, are not activated. Therefore, interference with the E6/ E6AP-mediated proteasomal degradation of p53 has been seen as another possible strategy for treatment.Theubiquitinationproteasome system (UPS) begins with theubiquitin activatingE1 molecules interactingwithE2conjugatingenzymes,followedbycatalyzationofthepolyubiqui‐ tination cascade onto target proteins by E3 enzymes [184]. A subset of E3s, called RING-finger E3s, are a group of ubiquitin ligases that have domains to which ubiquitination substrates bind, anditis thoughtthat by inhibiting this interaction,p53might bepreserved.Oneprominentp53 related RING-finger ubiquitin ligase is MDM2. MDM2 is normally expressed in a negative feedback manner to regulate p53 levels. Three dominant trains of thought have guided approaches seeking ways in which the negative effects of MDM2 might be neutralized: 1) Blocking activation domains on p53, 2) Increasing nuclear export of p53 so as not to activate MDM2 transcription, and 3) Inhibiting MDM2. Of these, the third approach has received the

targeted by inhibitors of E1 and/or E2, thereby limiting their usefulness [174, 175].

306 Human Papillomavirus and Related Diseases – From Bench to Bedside A Diagnostic and Preventive Perspective

even releasing pRB from E7 [181].

In summary, the scientific community has witnessed tremendous progress in the recent years towards the goal of eradicating HPV-mediated cervical carcinoma. Of these endeavors, routine Pap testing and the prophylactic vaccines, Gardasil and Cervarix, are particularly noteworthy fortheirdocumentedandanticipatedprogressindecreasingtheburdenofthisdisease.Improved vaccines are under development, as are better methods for early detection. Additionally, recent discoveriespertainingtotheHPVlifecycle,viralinfection,andimmuneclearancehaveprovided guidance toward educating the public about the biological and behavioral risk factors linked to cervical cancer. However, awareness among the populations of greatest risk, in both devel‐ oped and underdeveloped countries, is lacking. Although high-risk individuals may belong to diverseethnicgroupsand/orhavelowersocioeconomicstanding,theymaynotallbenefitequally from any single approach, necessitating the importance of targeted education and interven‐ tion. Thus, future initiatives for the prevention of cervical cancer must aim to decrease existing inequalities, with a strong emphasis on educating about HPV transmission and screening throughout a woman's lifetime, particularly in groups where incidence and death rates are disproportionate. The hope is that these preventive methods – and in particular, the vaccine – will significantly reduce the HPV disease burden for future generations.

**Author details**

ma Linda, CA, USA

**References**

USA

Whitney Evans1,3, Maria Filippova1

Medicine, Loma Linda, CA, USA

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2011;8:8. Epub 2011/06/30.

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Epub 2012/03/16.

, Ron Swensen2

1 Department of Basic Science, Loma Linda University School of Medicine, Loma Linda, CA,

2 Department of Gynecology and Obstetrics, Loma Linda University School of Medicine, Lo‐

3 Center for Health Disparities and Molecular Medicine, Loma Linda University School of

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and Penelope Duerksen-Hughes1

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309

Modern Molecular and Clinical Approaches to Eradicate HPV-Mediated Cervical Cancer

While progress in prevention must continue, complementary approaches that can provide better treatment options to populations that cannot directly benefit from vaccine-associated therapies must also be developed. These groups include women who are already infected with HPV, immunocompromised individuals such as those with HPV/HIV co-infections, and organ transplant patients. In treating these individuals, the prognosis and treatment of cervical cancer depends on our ability to medically diagnose and assign a disease stage. Therefore, improvements in diagnostic imaging, surgery, radiation therapy, chemotherapy, or a combi‐ nation thereof are being studied to give women more options and to enhance each patient's ability to make better-informed decisions.

Along with clinical treatment, molecular therapies that target cervical cancer processes are also anticipated to contribute to the elimination of cervical cancer. Research focusing on HPV early proteins will continue to provide insights regarding the viral mechanisms used to take control over cellular processes. Of these viral components, the E6 and E7 oncoproteins have long been recognized as the main mediators of HPV-associated malignancies. Therefore, the idea that approaches targeting these two oncoproteins are likely to act in an anti-oncogenic manner is quite reasonable. Such discoveries have the potential to exert a broad impact in the field of virology, as they will enable researchers to more fully understand virus-host interactions and how to better equip the body to respond to or even prevent infection.

In conclusion, cervical cancer research has come a long way, but there is still much more to be done to ensure that our accomplishments are not overshadowed by failures to educate, vaccinate, improve clinical management, and strengthen our knowledge about HPV. Indeed, it is quite possible that the challenge of HPV-mediated cervical cancer can be overcome in this generation, given the abundance of advancements, ideas and potential avenues that have been discussed here.
