Which entity is responsible for regulating the public accounting profession in the United States?

The Public Company Accounting Oversight Board (PCAOB) is the correct answer as it was specifically created by the Sarbanes-Oxley Act of 2002 to oversee the audits of public companies in order to protect the interests of investors. The PCAOB sets standards for auditing, monitors the quality of audits, and enforces compliance with its regulations and auditing standards. This makes it unique among the given options, as its primary focus is directly on public company audits, ensuring that auditors adhere to strict standards of integrity and independence.

In contrast, while the American Institute of CPAs (AICPA) plays a significant role in providing professional standards and supporting public accountants, it does not have the regulatory authority that the PCAOB has over public companies. The Securities and Exchange Commission (SEC) is a regulatory body that oversees securities markets and is concerned with investor protection, but it does not directly regulate the auditing profession itself. Lastly, the Internal Revenue Service (IRS) is responsible for tax administration and enforcement of tax laws, rather than the regulation of public accounting practices. This context illustrates why the PCAOB is the designated entity for regulating the public accounting profession in the United States.