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Table 1: List of HPV proteins and their function
HPV Function
proteins
Viral DNA replication
E1 Repressive agent in transcription
Inhibition of DNA replication [24,199]
DNA replication
Functions with E1, especially in HPV6, 11 and 16 [24]
Responsible for coding proteins regulating viral DNA transcription [199]
E2 cell transformation, initiating and inhibiting apoptosis, transcriptional regulation, and in the modulation of the
immortalizing and transformation poten-tial of HPV [24]
When inactive, it promotes E6 and E7 expression and influence tumor lesion development
When active, it inhibits E6 and E7 transciption leading to increased p53 expression and apoptosis of infected cells [199]
E4 Affects the formation of the HPV-1 triggered nodules may be involved in the cell cycle regulation [199]
[24]
E5 Transformation of viral DNA
Viral DNA replication
[24,199]
Maintains the viral replication
Synthesis of the genes via epithelium differentiation [200]
E6
Involved in HPV dependent malignant transformation via destructing the control of cell cycle regulation and cell
maturation [199]
Maintains the viral replication
Contributes to the genetic instability of HPV-infected cells by interfering with the normal replication of centrosomes
E7 Synthesis of the genes via epithelium differentiation [200]
Involved in HPV dependent malignant transformation via destructing the control of cell cycle regulation and cell
maturation [199]
HPV: human papillomavirus

may also be associated with human cancers. The current anus of the child via genital-finger transmission. [30]
understanding indicated that HPVs infect cells found in
germ layers of the skin and mucous membranes, keranocyte IMMUNE RESPONSES TO HPV AND
or cells with differentiation potential of keranocyte. The VACCINE-INDUCED PROTECTION
mechanism of HPV infection is suspected to be similar
among different tissues; in such the HPV infects the basal HPVs that cause persistent visible papillomas, especially
layer of the cervix causing exposure of the basement at oral and genital sites, are the main concern for the
membrane, and HPV enters the basal layer of the tonsillar individuals. It is known that under some circumstances the
epithelium infecting and exposing the crypt cells. [22,23] virus is cleared and although the underlying mechanism
of the virus clearance is not well understood, the immune
TRANSMISSION OF HPV response, particularly T cells, seems to play the main
role. [31-33] Lesion persistency and progression are increased
The most common sexually transmitted infection is in both animals and humans with genetic, iatrogenic or
presumed to be the HPV infection. HPV infection can be acquired cell mediated immune deficiencies, such as in
transmitted via both sexual and nonsexual contacts. HPVs patients with severe combined immunodeficiency, in
[34]
penetrate the body through the skin and epidermis injuries, immunosupressed organ recipient patients, in patients
[35]
mucous membranes and skin abrasions. Genital types with epidermodysplasia verruciformis and sun-exposed
[24]
[35]
of HPVs are mostly transmitted sexually. Generally in sites of patients with non-melanoma skin cancer. [35-37]
women, epidemiological studies have shown that the HPV Moreover, HPVs can escape the immune system and down
infection is associated with the number of sexual partners, regulate the innate immune signalling pathways. [38]
initial age of sexual intercourse and the likelihood of one of
the sexual partners with an HPV infection. [25,26] Therefore The clearance of high risk HPV types are believed to be
for HPV associated cancers, such as cervical, penile or harder since these types weaken the immune defences
urethra, the sexual partner plays a key role as much as the causing infection to continue and progress to neoplasias.
individual’s own sexual behaviour. [25,27] However, it should be noted that progression from
infections to cancer is a rare event and the first defence
More rarely, HPVs can be transmitted via perinatal against HPV is the natural immunity. High risk HPV
transmission during birth from the mother to child that is types are believed to destabilize the immune responses via
also observed in the transmission of other microbial and obstructing the interferon pathway, down regulating major
viral infections. [28,29] Horizontal transmission of HPV is histocompatibility complex class I genes and changing the
also possible and it was first reported with a 5 year old antigen production. High risk HPV types continue to
[39]
boy of HPV2 infection presented as warts on the hands and express the E6 and E7 oncoproteins that leads to genomic

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Journal of Cancer Metastasis and Treatment ¦ Volume 2 ¦ June 15, 2016 ¦