What is the Difference Between PCNA and Ki67

The key difference between PCNA and Ki67 is that PCNA is a nuclear protein that participates in DNA synthesis and repair pathways, while Ki67 is a nuclear protein that participates in cell proliferation and ribosomal RNA transcription.

Cell proliferation is a biological process that is essential to all living organisms. The control of this process is completely dysregulated in some types of cancers. Therefore, the assessment of cell proliferation in tumors has become a popular tool in diagnosing tumors. It also helps to choose the appropriate therapy for tumors. Cell proliferation markers are specific proteins whose presence in actively growing and dividing cells serves as an indicator for such cells. PCNA and Ki67 are two cell proliferation markers commonly used in diagnosing tumors.

1. Overview and Key Difference
2. What is PCNA
3. What is Ki67
4. Similarities – PCNA and Ki67
5. PCNA vs Ki67 in Tabular Form
6. Summary – PCNA vs Ki67

What is PCNA?

Proliferating cell nuclear antigen (PCNA) is a DNA clamp-type protein that acts as a processivity factor for the DNA polymerase delta in eukaryotic cells. It is extremely important for DNA replication. This protein is a nuclear protein that also plays a vital role in DNA repair. PCNA has a homotrimer structure. It normally achieves its processivity by encircling the DNA, where it acts as a scaffold to recruit other proteins involved in DNA replication, DNA repair, chromatin remodeling, and epigenetics.

Figure 01: PCNA

This nuclear protein has two main domains: PCNA interacting peptide (PIP) box and AlkB homolog 2 PCNA interacting motif (APIM). Many proteins interact with PCNA via these domains. The proteins binding to PCNA via the PIP box are involved in DNA replication. On the other hand, the proteins binding to PCNA via APIM are involved in genotoxic stress. Moreover, this protein is elevated during the G1/S phase of the cell cycle. Quiescent cells have very low levels of PCNA. Therefore, PCNA expression can be used as a marker of cell proliferation because cells remain a long time in the G1/S phase when proliferating.

What is Ki67?

Ki67 is a nuclear protein involved in cell proliferation and ribosomal RNA transcription. It is also known as antigen Ki-67 or MKI67. It is a nuclear protein encoded by the MK167 gene in humans. This nuclear protein is associated with cellular proliferation. It is also associated with ribosomal RNA transcription. The inactivation of KI67 is responsible for the inhibition of ribosomal RNA synthesis. Moreover, Ki67 is a classical marker for cellular proliferation.

Figure 02: Ki67

During interphase, ki67 antigen can be detected within the cell nucleus, while in mitosis, it is relocated to the surface of the chromosomes. Furthermore, ki67 is present during all active phases of the cell cycle (G1, S, G2, and mitosis). However, it is absent in resting quiescent cells. In breast cancer, the ki67 immunohistochemistry test can detect how quickly breast cancer cells divide. In breast cancer, the ki67 test identifies a high proliferative subset of patients with ER-positive breast cancer who can obtain greater benefits from chemotherapy.

What are the Similarities Between PCNA and Ki67?

PCNA and Ki67 are two cell proliferation markers commonly used in diagnosing tumors.
Both proteins are highly expressed in proliferating cells.
These proteins can be detected in the G1 and S phases of the cell cycle.
They are nuclear proteins that are made up of amino acids.
Their expression can be detected through immunohistochemistry.

What is the Difference Between PCNA and Ki67?

PCNA is a nuclear protein involved in DNA synthesis and repair pathways, while Ki67 is a nuclear protein involved in cell proliferation and ribosomal RNA transcription. Thus, this is the key difference between PCNA and Ki67. Furthermore, PCNA gene codes for PCNA in humans, while MK167 gene codes for Ki67 in humans.

The below infographic presents the differences between PCNA and Ki67 in tabular form for side by side comparison.

Summary – PCNA vs Ki67

The proliferative activity of tumor cells is an important prognostic marker in the diagnosis of cancer. PCNA and Ki67 are two commonly used cell proliferation markers in diagnosing tumors. PCNA is a nuclear protein involved in DNA synthesis and repair pathways, while Ki67 is a nuclear protein involved in cell proliferation and ribosomal RNA transcription. So, this is the summary of the difference between PCNA and Ki67.

Reference:

1. “Proliferating Cell Nuclear Antigen.” An Overview | ScienceDirect Topics.
2. JN;, Li LT;Jiang G;Chen Q;Zheng. “KI67 Is a Promising Molecular Target in the Diagnosis of Cancer (Review).” Molecular Medicine Reports, U.S. National Library of Medicine.

Image Courtesy:

1. “Pcna holiday dna” By Opabinia regalis – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Ki67-Tubulin” By GerryShaw – By appropriate cell culture and stainingPreviously published: Own Website (pending) (CC BY-SA 4.0) via Commons Wikimedia

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